Glossary

  • 1

    100,00 GWP
    The global warming potential (GWP) of a greenhouse gas over 100 years.

  • 2

    2 °C Scenario
    A scenario developed by the IEA to demonstrate the actions needed in the energy sector to limit the rise in global temperatures to no more than 2 °C. Following the Paris Agreement on Climate Change in 2015, in which countries agreed on a more ambitious temperature target, It is no longer part of the IEA’s scenario analyses.
    20,00 GWP
    The global warming potential (GWP) of a greenhouse gas over 20 years.

  • A

    Abated fossil fuels
    See fossil fuels with CCUS.
    Acid gas removal
    See gas treatment.
    Active solar thermal
    Heating of a heat transfer liquid or gas (typically air) as a means of transferring solar radiation for space heating, often coupled with central heating and heat storage in a tank or masonry. In air-based systems, solar air collectors are often integrated into walls or roofs, for example a tile roof with air flow paths built into it to make use of the heat absorbed by the tiles.
    Additive
    A non-hydrocarbon substance added to or blended with an oil product to modify its properties, such as its combustion characteristics (octane, cetane) or cold flow properties. Includes: oxygenates, such as alcohols (methanol, ethanol); ethers such as MTBE (methyl tertiary butyl ether), ETBE (ethyl tertiary butyl ether) and TAME (tertiary amyl methyl ether); esters (e.g. rapeseed or dimethylester); and chemical compounds (such as tetramethyl lead, tetraethyl lead and detergents).
    In IEA statistics, the bioenergy fractions of biogasoline, biodiesel and ethanol destined for fuel use are not counted as additives, but as liquid biofuels. However, they are included as additives in the Oil Information publication.
    Advanced bioenergy
    Sustainable fuels produced from wastes, residues and non-food crop feedstocks (excluding traditional uses of biomass), which are capable of delivering significant life cycle greenhouse gas emissions savings compared with fossil fuel alternatives and of minimising adverse sustainability impacts. Advanced bioenergy feedstocks either do not directly compete with food and feed crops for agricultural land or are only developed on land previously used to produced food crop feedstocks for biofuels.
    Advanced economy
    OECD regional grouping and Bulgaria, Croatia, Cyprus, Malta and Romania
    Advanced gas-cooled reactor
    A type of nuclear fission reactor with a graphite moderator and carbon dioxide coolant. Designed and operated in the United Kingdom, and developed from the Magnox reactor. Retains the graphite moderator and carbon dioxide coolant of the Magnox design, but increased the cooling gas temperature to create more efficient steam conditions. The final steam conditions at the boiler stop valve are similar to those in a conventional coal-fired power station, allowing for the use of the same turbo-generator power plant. The first prototype became operational in 1962 at Windscale, but the first AGR did not become commercially operational until 1976. In total, 14 AGRs were built.
    Aframax
    Seagoing tankers with a deadweight between 75 000 and 119 999 tonnes. Aframaxes tend to carry dirty cargoes, most often in parcel sizes of 70 000 or 80 000 tonnes (500 000 or 700 000 barrels). Typical routes include Caribbean exports to the US Gulf, lightering movements in the US Gulf, North African exports to Southern Europe, North Sea and Baltic exports to Northern Europe and South East Asian exports to the Far East.
    Agriculture, forestry and other land use (AFOLU)
    A sector included in greenhouse gas accounting frameworks which encompasses managed ecosystems. AFOLU emissions include greenhouse gas emissions from agriculture, land use, land-use change and forestry.
    Air source heat pump
    A heat pump that can absorb heat from air outside a building and release it inside; it uses the same vapour-compression refrigeration process and much the same equipment as an air conditioner, but in the opposite direction. Includes air-to-air and air-to-water heat pumps.
    Air-to-air heat pump
    Electricity-driven heating devices that use heat from the outside air to heat a building through in-room blowers or vents. Ideal for buildings without radiators or underfloor heating, they can also provide space cooling. Some models can be combined with water tanks to provide domestic hot water. Run on electricity, and when installed in well-insulated buildings, can achieve significant energy bill savings – for example, up to 35% in Germany, or up to 50% in France, when compared to gas boilers. Average lifespan before replacement is 12-15 years. See Heat pump.
    Air-to-water heat pump
    Electricity-driven heating devices that use heat from the outside air to heat water for radiators or underfloor heating. Usually connected to a tank that provides hot water for heat distribution systems, bathrooms, and kitchens. Some models also provide space cooling. Run on electricity, and when installed in well-insulated buildings, can achieve significant energy bill savings – for example, up to 35% in Germany or up to 50% in France, when compared to gas boilers. Average lifespan before replacement is 15-18 years. See Heat pump.
    Alkaline electrolysis
    A type of electrolysis that uses nickel-based electrodes and a concentrated alkaline solution to enable the splitting of water. Alkaline electrolysers have been applied on a 10 MW+ scale for more than a hundred years. Traditionally used with hydropower or grid electricity and operated in a baseload manner to produce hydrogen for ammonia plants until gas reforming became the cheapest technology. Both atmospheric and pressurised versions exist.
    Alkylation
    A refining process for chemically combining isobutane with olefinic hydrocarbons (e.g. propylene, butylene) through the control of temperature and pressure in the presence of an acid catalyst, usually sulphuric acid or hydrofluoric acid. The product, alkylate (an isoparaffin) has a high octane value and is blended into motor and aviation gasoline to improve the anti-knock value of the fuel.
    Alternating current (AC)
    An electric current that periodically reverses direction and changes its magnitude continuously with time. This is in contrast to direct current (DC), which flows only in one direction. It is the form of electrical energy that is conveyed by most transmission and distribution systems and therefore the type that is used in most household appliances. AC is produced by rotating electricity generators such as those in coal, gas, biomass and wind power plants. Solar PV electricity generators and batteries produce DC and require inverters to convert the output to AC. Most electric power is generated at either 50 or 60 Hertz, which is a measure of the frequency with which the current changes direction.
    Ammonia
    A compound of nitrogen and hydrogen (NH3) that is an industrially produced input to much of the world's fertiliser manufacture, resulting in substantial CO2 emissions from the use of fossil fuel inputs to generate the input hydrogen. With properties similar to liquefied petroleum gas (LPG), ammonia can also be used directly as a fuel in direct combustion processes, as well as in fuel cells, and can be "cracked" to release its hydrogen content. As it can be made from low-emissions hydrogen, ammonia has the potential to be a low-emissions fuel if the production process (including nitrogen separation) is powered by low-emissions energy. Produced in such a way, ammonia is considered a low-emissions hydrogen-based liquid fuel.
    Amsterdam-Rotterdam-Antwerp
    A basis for estimating oil trade metrics in Northwest Europe that compiles data on spot transactions from the ports of Amsterdam, Rotterdam and Antwerp. The three ports are close enough to one another and busy enough to be considered interchangeable. Trades in the Northwest European hub are often referred to as being on an "ARA basis".
    Announced Pledges Scenario (APS)
    An IEA scenario which assumes that all climate commitments made by governments and industries around the world as of the end of August 2023, including nationally determined contributions (NDCs) and longer-term net zero targets, as well as targets for access to electricity and clean cooking, will be met in full and on time.
    Anthracite
    A high-rank hard coal with a gross calorific value (moist, ash-free basis) greater than or equal to 24 MJ/kg and a mean random vitrinite reflectance greater than or equal to 2%.
    Anthropogenic
    Arising from human activity. For example, anthropogenic greenhouse gas emissions are those emissions that would not have arisen had it not been for human activities.
    Anti-knock
    The resistance to detonation in spark-ignition or compression-ignition internal combustion engines. The anti-knock value is measured in terms of octane number for gasoline engines and cetane number for diesel fuels.
    API gravity
    The American Petroleum Institute gravity is a measure of how heavy or light a petroleum liquid is compared to water. If the API gravity is greater than 10°, it is lighter and floats on water. If less than 10°, it is heavier and sinks. The formula to calculate API Gravity is (141.5/specific gravity at 60 °F) - 131.5. See also sweet crude, sour crude and total acid number.
    Apparent demand for oil
    An estimate in IEA oil market reporting of domestic demand (as opposed to counting barrels whose actual delivery has been reported and documented). Calculation varies by country. For example, in China, apparent demand is defined as refinery output plus net product imports (adjusted for fuel oil and direct crude burning, smuggling and stock changes).
    Aquifer
    An underground water reservoir. If the water contains large quantities of minerals, it is a called a saline aquifer. Saline aquifers are used for geological CO2 storage.
    Aromatics
    A class of unsaturated cyclic hydrocarbons such as benzene, toluene and xylene produced within refineries and jointly referred to as BTX or, commercially, hydrogenated pyrolysis gasoline (HPG). Commercial uses include fuel additives, paints, coatings, cleaning agents, foams and polymers.
    Asphalt
    A product used in the construction of roads and as a roofing material. Produced by heating, drying and mixing aggregate and sand with bitumen, a heavy output of crude oil refining. In energy statistics, the asphalt category includes fluidised and cut back bitumen.
    Associated gas
    Natural gas produced in association with crude oil.
    Asynchronous generation
    Any electricity generator in which the waveform of the generated voltage is not synchronised with the rotation of the generator (i.e. is not synchronous). The output frequency of a synchronous generator can be more easily regulated to remain at a constant value, for example to set the frequency of the electricity grid, and thereby provide so-called "inertia" to the grid to help maintain its target frequency. Asynchronous generators do not have these characteristics. A simple type of asynchronous generator is an induction generator for a wind turbine, which uses the signal from the electricity grid to which it is connected as its frequency and phase reference; it therefore relies on the proper operation of external synchronous generators for its own operation. Solar photovoltaic generators use inverters to convert direct current electricity to alternating current electricity for grid connection and this is also asynchronous. However, some smart inverters have been developed that can assist with grid frequency regulation.
    Atmospheric residue
    The heavy residual liquid from the atmospheric distillation of crude oil at a refinery. See also vacuum residue and cracked residue.
    Average net calorific value
    A measure of energy content reported per unit of mass on a lower heating value (LHV) basis. In energy statistics, average net calorific value is specified for fuels that have variable energy content, such as primary and secondary oil products, liquid biofuels and charcoal.
    Aviation fuel
    A fuel prepared especially for aircraft propulsion. Includes gasoline-type jet fuel (aviation gasoline), kerosene-type jet fuel, sustainable aviation fuel and hydrogen-based synthetic kerosene (see hydrogen-based synthetic liquid fuel).
    Aviation gasoline
    A motor spirit prepared especially for aviation piston engines, with an octane number suited to the engine, a freezing point of -60 °C and a distillation range usually within the limits of 30 °C and 180 °C. Also known as avgas or aviation spirit.

  • B

    Backhaul
    A term used in oil trade. Backhaul voyages occur when cargo is moved on the return leg of a journey. As charter rates incorporate the return ballast leg of a journey, backhaul opportunities represent a chance to make supplementary income for tanker owners. For example, a vessel could load in West Africa and head east on its return from a laden voyage from the Arabian Gulf to Europe or North America.
    Backup power
    A form of independent power generation capacity that, in the event of disruption, can provide electricity to households and businesses connected to the main power grid. Backup generators are typically fuelled by diesel or gasoline, but can also be fuel cells running on gaseous fuels. Capacity can be as little as a few kilowatts. Such capacity is distinct from mini-grid and off-grid systems that are not connected to a main power grid. The term is sometimes also applied to capacity on the power grid that is available to help meet peak demand or compensate for unforeseen drops in supply from other sources, including, for example, wind power. In this case, dispatchable or flexible power capacity are more commonly used terms. See dispatchable generation.
    Backwardation
    The oil market is said to be in backwardation when the price of futures or physicals contracts for near delivery months is higher than for more distant months. The reverse situation is known as contango.
    Bagasse
    The residue remaining after the sugar-containing juice used in bioethanol production has been extracted from plants like sugar cane. Bagasse can be burned to provide a renewable source of heat, for example at biorefineries. See biorefining.
    Ballast
    A term used in oil trade. Seawater that is pumped into a vessel’s empty tanks to submerge the vessel sufficiently to operate correctly. A ballast journey refers to one where cargo is not carried, often the return leg of a laden voyage.
    Barges
    A term used in oil trade. Flat-bottomed boats used to carry cargo on inland waterways. Often used in the process of lightering to transfer cargoes from larger vessels to terminals only accessible to smaller boats.
    Barrel of oil equivalent (boe)
    A unit of energy equal to the energy contained in the volume of crude oil filling one standard oil barrel, which is 42 US gallons or 158.987 litres. One boe is equivalent to 5.68 GJ.
    Barrels per day (b/d)
    The volume of oil consumed or produced in one day, expressed in terms of a standard barrel of crude oil. Often used to express the average daily demand over a fixed period, such as a year. When expressed as boe per day, this unit can be used for any type of energy converted on the basis of 5.68 GJ per boe.
    Basis
    The differential between a spot or “cash” price and the nearest equivalent futures price. Basis is normally quoted as cash minus futures price. A positive number indicates a futures discount; a negative number indicates a futures premium. In oil trade, basis may also refer to the price differentials of a commodity in different locations or between different products (e.g. kerosene in the physical market and gasoil in the futures market).
    Battery (electrochemical)
    A device consisting of one or more electrochemical cells for the storage of electricity and the powering of electrical devices. Consists of an electrode (an anode and a cathode) and an electrolyte. When the anode and cathode are connected to an external electric load, a redox reaction converts high-energy reactants to lower-energy products, and the free-energy difference is delivered to the external circuit as electrical energy. Batteries that are capable of multiple charge–discharge cycles may be recharged by being connected to an external power source, in which case electrons flow through the electrolyte in the opposite direction, leading to the inverse redox reaction.
    Battery electric vehicle (BEV)
    A road vehicle deriving all of its motive power from electricity stored in a battery with no onboard gaseous or liquid fuel consumption.
    Becquerel
    The SI unit of radioactivity, defined as the activity of a quantity of radioactive material in which one nucleus decays per second.
    Behind-the-meter
    Electrical equipment that is situated on the consumer's side of an electricity meter and usually under the consumer's control. Includes: rooftop solar PV; residential and industrial batteries or generators; energy management systems and demand response controls; on-site electrolysers in industry and refining. See also: in-front-of-the-meter.
    Beyond 2DS
    A variant of the IEA 2 °C Scenario (2DS) that was used for analysis in the IEA Energy Technology Perspectives 2017 publication. The B2DS looked at how far known clean energy technologies could go if pushed to their practical limits, in line with carbon neutrality by 2060 to limit future temperature increases to 1.75 °C by 2100, the midpoint of the Paris Agreement’s ambition range. See also 2 °C Scenario, Stated Policies Scenario, Announced Policies Scenario and Net Zero Emissions Scenario.
    Billion cubic feet
    One billion cubic feet is 28.3 million cubic metres.
    Billion cubic feet per day (Bcf/d)
    One billion cubic feet is 28.3 million cubic metres.
    Billion cubic metres (bcm)
    A unit of energy equal to the energy contained in one billion cubic metres of a standardised gaseous fuel, such as natural gas, at a given temperature and pressure. One bcm of natural gas is equivalent to 36 PJ on a lower heating value (LHV) basis.
    Billion cubic metres equivalent
    An energy unit equivalent to a billion cubic metres of natural gas (36 PJ LHV)
    Billion cubic metres per day
    The volume of a gaseous fuel consumed or produced in one day, expressed in terms of a standard cubic metre of the gas (e.g. natural gas). Often used to express the average daily demand over a fixed period, such as a year. When expressed as bcm of natural gas per day, this unit can be used for any type of energy converted on the basis of 36 PJ per bcm (LHV).
    Binary cycle
    A type of power generator in which the turbine is driven by a separate working fluid from the input working fluid. Binary cycles are most commonly employed in geothermal power plants, in which a heat exchanger transfers the heat from the hot water emanating from the underground reservoir to a working fluid with a lower boiling point than water, such as isobutane, pentane or ammonia. Binary cycles permit electricity generation from geothermal resources at temperatures below 180 °C, for which flash cycles and double flash cycles are not generally viable.
    Bio-based synthesis gas
    One of the biogases. A synthesis gas produced by the thermal treatment of biomass feedstocks and composed of hydrogen and carbon monoxide. It can be used as a fuel or as an input to the production of chemicals or liquid and gaseous fuels.
    Biodiesel
    Diesel-equivalent fuel made from the transesterification of vegetable oils and animal fats, hydrogenated vegetable oil (HVO), thermal processes such as gasification and fermentation. To be a low-emissions fuel, the non-bioenergy inputs (such as hydrogen for HVO, or methanol for transesterification) must be from low-emissions hydrogen.
    Bioenergy
    Energy content in solid, liquid and gaseous products derived from biomass feedstocks and biogas. Includes solid bioenergy, liquid biofuels and biogases.
    Bioenergy equipped with CCUS
    The use or production of bioenergy products in a manner that prevents the CO2 generated by the combustion, oxidation or fermentation process from reaching the atmosphere and contributing to climate change. As the carbon that is captured is biogenic in origin (i.e. it has integrated into plant-based matter relatively recently, often within the previous 1-2 years), it can be said to have been removed from the atmosphere to reduce total atmospheric greenhouse gas levels if it is permanently kept from the atmosphere, for example by geological CO2 storage. See CCUS.
    Bioenergy with carbon capture and storage
    Bioenergy with carbon capture and storage, or BECCS, involves capturing and permanently storing CO2 from processes where biomass is converted into fuels or directly burned to generate energy. Because plants absorb CO2 as they grow, this is a way of removing CO2 from the atmosphere.
    Bioenergy with carbon capture and utilisation
    See bioenergy equipped with CCUS.
    Bioethanol
    Ethanol produced from biomass and/or biodegradable fraction of organic waste.
    Biofuels
    See liquid biofuels.
    Biogas
    A mixture of methane, CO2 and small quantities of other gases produced by anaerobic digestion of organic matter in an oxygen-free environment. It includes landfill gas and sewage sludge gas, and it can be upgraded by removing non-methane constituents, principally CO2.
    Biogases
    A group of gases that includes biogas, biomethane and bio-based synthesis gas. Biogases are used mainly as fuels, but can also be used as chemical feedstocks, for example in processes that use natural gas inputs.
    Biogenic waste
    The fraction of waste classified as biomass and renewable, i.e. derived from food, agriculture or other organic matter. In the absence of more accurate data, the biogenic waste fraction is sometimes assumed to be 50% of municipal solid waste by energy content. See also municipal solid waste (renewables) and non-biogenic waste.
    Biomass carbon removal and storage
    A range of processes that use plants and algae to remove CO2 from the atmosphere and store that CO2 underground or in long-lived products.
    Biomass integrated gasification and combined cycle
    A type of integrated gasification combined cycle in which the fuel input is solid bioenergy.
    Biomass-to-coal (BTC)
    A process that mimics the long-term natural process of coal formation. It typically uses solid bioenergy inputs and methods such as hydrothermal carbonisation to remove moisture and other unwanted components.
    Biomass-to-liquids
    A process for making liquid biofuels from solid bioenergy. It typically involves gasification of the biomass to synthesis gas followed by synthesis to liquid products (such as diesel, naphtha or gasoline) via either the Fischer-Tropsch route or the methanol-to-gasoline route. The process is similar to those used in coal-to-liquids and gas-to-liquids.
    Biomethane
    Biomethane is a near-pure source of methane produced either by “upgrading” biogas (a process that removes any carbon dioxide and other contaminants present in the biogas) or through the gasification of solid biomass followed by methanation. It is also known as renewable natural gas.
    Biomethanol
    Methanol produced from biomass without carbon inputs from fossil fuels.
    Biorefining
    The process of refining biomass to commercial energy and/or chemical products. This process may include multiple refining steps undertaken separately, with the transfer of intermediate outputs between them. Biorefining processes can include pretreatment, fermentation, gasification, pyrolysis and upgrading. Usually takes place in a biorefinery.
    Bitumen
    A solid, semi-solid or viscous hydrocarbon with a colloidal structure, being brown to black in colour. It is obtained as a residue in the distillation of crude oil and by vacuum distillation of oil residues from atmospheric distillation. It should not be confused with the nonconventional primary extra-heavy oils, such as oil sands, which may also be referred to as bitumen. See also extra-heavy oil and bitumen.
    Bituminous coal
    A medium-rank hard coal with either a gross calorific value (moist, ash-free basis) not less than 24 MJ/kg and with a mean random vitrinite reflectance less than 2%, or a gross calorific value (moist, ash-free basis) less than 24 MJ/kg provided that the mean random vitrinite reflectance is equal to or greater than 0.6%.
    Black liquor
    The alkaline-spent liquor obtained from the digesters during the production of the sulphate or soda pulp required for paper manufacture.
    Blast furnace gas
    The by-product gas of blast furnace operation, consisting mainly of nitrogen, carbon dioxide and carbon monoxide.
    Blend wall
    The maximum amount of an additive that is blended into a fuel product, for example liquid biofuels into conventional, oil-based refined products. The limit may be due to factors such as logistical and infrastructural shortcomings or economic viability.
    Blowdown capture
    Processes conducted at wellheads or elsewhere along the oil and gas supply chain when equipment (e.g. vessels, compressors) must be depressurised. Blowdowns can be triggered by emergency signals or routine start-up or shutdown procedures. When this happens, operators open up the well to remove the liquids and gas. Emissions are mitigated when excess gas is recovered and used on-site or sent to the sales line, instead of being vented or flared.
    Boiling water reactor
    A type of nuclear power plant, introduced in the 1950s, in which water is heated directly by the reactor core to produce steam that drives a turbine to generate electricity. This system is different from that of a pressurised water reactor (PWR), which has a separate loop for the water that drives the turbine and the water that circulates through the reactor. As of 2020, the capacity of the world's operational BWRs was 64 GWe, second to PWRs and 16% of all operational nuclear generators.
    British thermal unit (Btu)
    A measure of energy content. Defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. One Btu is equivalent to 1.055 joules. One MBtu is one million Btu, equivalent to 1.055 MJ. The notation MMBtu is sometimes used for metric million Btu, which is the same as MBtu.
    Brown coal
    Coal with a gross calorific value (moist, ash-free basis) less than 24 MJ/kg and a mean random vitrinite reflectance less than 0.6%. Brown coal comprises sub-bituminous coal and lignite.
    Brown coal briquettes
    A composition fuel manufactured from lignite, produced by briquetting under high pressure with or without the addition of a binding agent. In IEA statistics, "energy industry own use" includes consumption by briquetting plants. See also hard coal briquettes.
    BTX aromatics
    See aromatics.
    Build absolutely nothing anywhere near anybody
    An expression used to caricature the apparent opposition of certain people or communities to any proposed project, even if the failure to build at least one type of installation could jeopardise their own access to secure energy.

  • C

    Calcined coke
    A petroleum coke or coal-derived pitch coke obtained by the heat treatment of green coke to about 1 330 °C. Normally has a hydrogen content of less than 0.1% by weight.
    Calorie (cal)
    A unit of energy equal to the amount of heat needed to raise the temperature of one gramme of water by 1 °C (or one kelvin). One calorie is equivalent to 4.184 joules. However, when used in measurements of the energy content of food, a different definition is typically used in which one calorie is equivalent to 4.184 kJ.
    Calorific value (CV)
    A standardised measurement of the heat obtained from one unit of a fuel. Also known as the heating value. Allows the energy contained in different fuels to be compared and summed. Calorific and heating values can be expressed in any energy unit, with joules being the most common. Calorific and heating values can be expressed as lower heating values (LHV) and higher heating values (HHV)
    CANDU
    See pressurised heavy water reactor.
    Capacity
    The amount of energy output or input that can be sustained by a piece of energy-related equipment over a given period of time. Typically reported in watts, though "barrels per day" is commonly used in the oil industry. Nameplate capacity (also called rated capacity, nominal capacity, installed capacity, maximum effect or gross capacity) typically refers to the full-load operation intended by the designer and guaranteed by the equipment manufacturer. In reality, actual operation can usually exceed the nameplate capacity if required over short periods.
    Capacity credit
    The proportion of the nameplate generating capacity of an electrical generator that can be reliably expected to generate electricity during times of peak demand on the grid to which it is connected. The sum of all capacity credits across an electricity system is useful as an approximation of the firm power that the system can reliably provide at a given time.
    Capacity factor
    The ratio of the average output of a plant to its nameplate maximum capacity during a certain prescribed period of time. Can be applied to electricity generating plants, fuel production facilities, factories and other installations. Expressed as a percentage. Also known as the load factor.
    Capital costs
    See capital expenditure.
    Capital expenditure
    The cost of developing and constructing a fixed asset such as a power plant or grid infrastructure. Typically incurred before the asset enters operation. Includes the purchase cost of hardware and land, plus the project costs of delivery, installation, logistics and regulatory expenses, such as permitting. Excludes the cost of capital. In IEA modelling, total power generation capital expenditure includes refurbishment and decommissioning of assets in addition to their deployment. Can be expressed on an overnight basis or on the basis of actual expenditure per period of project execution. IEA investment estimates are expressed as the latter unless otherwise stated.
    Carbon capture, utilisation and storage (CCUS)
    The process of capturing carbon dioxide emissions from fuel combustion, industrial processes or directly from the atmosphere. Captured CO2 emissions can be stored in underground geological formations, onshore or offshore, or used as an input or feedstock in manufacturing.
    Carbon dioxide (CO2)
    A gas consisting of one part carbon and two parts oxygen. It is an important greenhouse (heat-trapping) gas.
    Carbon dioxide equivalent CO2-eq)
    A standardised metric for the contribution to climate change exerted by different greenhouse gases, expressed in terms of the contribution that is made by one unit of CO2. Usually expressed in terms of GWP100. Allows comparison and summing of the contributions of different emissions.
    Carbon dioxide removal
    The reduction of the atmospheric concentration of CO2 through human intervention. Approaches to CDR include bio-based CDR techniques and engineered CDR technologies (sometimes called carbon removal technologies, or CRTs), including direct air capture. CDR methods are sometimes referred to as negative emissions technologies (NETs) because they are a necessary component of a system that can achieve "net negative emissions", i.e. when CDR exceeds emissions to the atmosphere in a given period.
    Carbon market
    An arena for the organised transaction of certified avoided greenhouse gas emissions or certificates that permit the emission of greenhouse gases. Generally overseen by governments as a cost-efficient means of ensuring compliance with emission goals, but can also be used in voluntary markets whereby buyers offset their emissions.
    Carbon monoxide (CO)
    A gas consisting of one part carbon and one part oxygen. It is a main component of synthesis gas (syngas) along with hydrogen. It is a product of the incomplete combustion of carbon-containing fuels. It is a colourless, odourless, tasteless and poisonous gas that can cause severe health problems if inhaled.
    Cash market
    In oil trade, the market in which physical oil is traded (e.g. the Rotterdam spot market).
    Cash price
    See spot price.
    Cash settlement
    In oil trade, a cash payment to close a futures contract (e.g. Brent on the Intercontinental Exchange.
    Catalytic cracking
    A refining process that breaks down the larger, heavier and more complex hydrocarbon molecules into simpler and lighter molecules by the action of heat aided by the presence of a catalyst, but without the addition of hydrogen. In this way heavy oils (fuel oil components) can be converted into lighter and more valuable products (notably gasoline and middle distillate components).
    Catalytic reforming
    A chemical process used in oil refining to convert the fractions of crude oil that have a low octane rating into reformates, which are high-octane liquid products blended into high-octane gasoline. A high-temperature process, operating between 495 °C and 525 °C and under pressures of 5 to 45 atmospheres. Catalytic reformers are not found in the simplest (topping) refineries, but may be present in hydro-skimming, conversion or deep conversion refineries, in order of refinery complexity.
    Cetane number
    An indicator of the combustion speed of diesel fuel. Equal to the percentage by volume of cetane in the mixture, with reference to the fuel alpha-methyl-naphthalene, which has a cetane number of zero. A higher cetane number signifies a shorter ignition delay. The octane number performs a similar function for the gasoline market as the cetane number does for diesel. See anti-knock.
    Cetane rating
    See cetane number.
    Charcoal
    The solid residue from the carbonisation of wood or other vegetal matter through slow pyrolysis.
    Charter
    The lease of a ship for anything from a single voyage (spot charter) to a fixed period of time (time charter, most commonly one or three years). Commonly used in oil and gas trade.
    Charter rate (or Freight rate)
    The agreed cost of hiring a tanker. In oil trade, spot charter rates are tariffs for the carriage of a single cargo from one specified port to another (including the return ballast journey) in the immediate future (generally within the next six weeks). Spot rates typically include all expenses of operating the vessel, from fuel to crew, but exclude costs related to the cargo (e.g. inspection fees). Time charter rates are a daily rate of hire over a fixed period, in which tanker owners pay for vessel expenses (such as maintenance and vessel insurance) and the charterer pays for voyage costs (such as bunker fuel).
    Chemical compounds
    In energy statistics, compounds added to oil products, including tetramethyl lead, tetraethyl lead and detergents. Quantities of ethanol in this category relate to the quantities destined for fuel use only.
    Chemical feedstock
    Physical energy products used as raw materials to produce chemical products, typically in the petrochemical sector. Examples are crude oil-based ethane or naphtha to produce ethylene in steam crackers.
    Circulating fluidised bed
    A type of combustion technology that uses a fluidised bed with a recirculating loop for greater efficiency and reduced emission of pollutants.
    Clean cargo
    In oil trade, includes gasoline, middle distillates and other light petroleum products. Carried in smaller, more expensive clean product tankers or barges.
    Clean cooking systems
    Cooking solutions that release less harmful pollutants, are more efficient and environmentally sustainable than traditional cooking options that make use of solid biomass (such as a three-stone fire), coal or kerosene. This refers to improved cook stoves, biogas/biodigester systems, electric stoves, liquefied petroleum gas, natural gas or ethanol stoves.
    Clean energy
    An umbrella term that groups energy sources, infrastructure, applications and related assets that are compatible with a net zero emissions energy system. The IEA uses this term primarily to sum all the investments related to clean energy. The categories of investment include: in power, generation from renewable sources, nuclear and fossil fuels fitted with CCUS, plus battery storage and electricity grids; in efficiency, energy efficiency in buildings, industry and transport, excluding aviation bunkers and domestic navigation; in end-use applications, direct use of renewables, electric vehicles, electrification in buildings, industry and international marine transport, plus use of hydrogen, hydrogen-based fuels, CCUS in industry and direct air capture; and in fuel supply, low-emissions fuels, liquid biofuels and biogases and hydrogen-based fuels.
    Clean energy innovation
    The process of developing a new clean energy technology, from initial idea, through R&D and prototyping, to demonstration and product development. All technology designs that reach the market pass through these stages (denoted by their Technology Readiness Level), but most initial ideas never become saleable products or processes. Given the public good status of clean energy technologies and the externalities associated with climate change, government support plays a central role in clean energy innovation and addressing barriers such as the so-called valley of death.
    Clean Energy Ministerial
    A multilateral forum that convenes a community of the world's largest and leading countries, companies and international experts to accelerate clean energy transitions. Its members (as of 2023) are 28 national governments and the European Commission, which together represent 90% of the world’s clean power and 80% of global clean energy investment. See http://www.cleanenergyministerial.org.
    Clean energy technology
    A technology that has the potential to help increase the uptake of clean energy. Includes any device, component of a device or process for its use dedicated to producing, storing or distributing energy with low CO2 emissions intensity; or a device that provides an energy service or energy commodity that enables users to minimise their contributions to atmospheric CO2 concentrations in line with net zero emissions globally. Includes technologies that reduce the cost or improve the performance of manufacturing other clean energy technologies. Clean energy technologies overlap considerably with the range of technologies frequently grouped together as “cleantech” or “climate tech”. However, these other classifications are broader than energy-related technologies. See also: technology application; technology type; technology design; and technology component.
    Clean innovation
    See clean energy innovation
    Climate change
    A change in climate (e.g. regional temperature, precipitation, weather event intensity) caused by an intensification of the greenhouse effect, in large part due to the accumulation of greenhouse gases in the atmosphere. Also called global warming or global heating.
    Closing price
    In oil trade, the price at the close of trading.
    Co-generation (or combined heat and power)
    The simultaneous generation of both electricity and heat from the same fuel, with both products directed to useful purposes. Energy inputs can include (inter alia) coal, bioenergy, natural gas, nuclear material, solar energy or geothermal. Enables much higher efficiencies of fuel use than the generation of electricity or heat alone. Most commonly employed for district heating or industrial utilities, typical plants are 10 MW to 100 MW. However, plants of over 500 MW are in operation, and technologies for buildings (several kW of capacity) also exist.
    CO2 intensity
    A measure of the amount of CO2 (or other greenhouse gases) emitted during the supply of one unit of an energy product, a manufactured good, a received service or economic activity. Enables the comparison of similar goods on an environmental basis, but can vary by the extent to which scope 1, scope 2 and scope 3 emissions are included in the estimation.
    CO2 venting
    The intentional release to the atmosphere of CO2 from industrial processes that require the separation of CO2 from other gases. These processes include: the processing of raw natural gas to remove CO2 and other impurities that cannot be fed into the pipelines of liquefaction units; fermentation processes such as the production of bioethanol; the upgrading of biogas to biomethane; and the water-gas shift reaction to increase hydrogen yield from hydrocarbon inputs. In many cases and at relatively low cost, CO2 that would otherwise be vented can be compressed and stored via CCUS so that it cannot contribute to climate change. As of 2022, around 25 Mt per year of CO2 from natural gas processing is injected into geological formations.
    Coal
    Consists of both primary coal, i.e. lignite, coking and steam coal, and derived fuels, e.g. patent fuel, brown-coal briquettes, coke-oven coke, gas coke, gas works gas, coke-oven gas, blast furnace gas and oxygen steel furnace gas. Peat is also included.
    Coal seam gas
    See coalbed methane.
    Coal seam methane
    See coalbed methane.
    Coal tar
    The liquid by-product of the carbonisation of coal in coke ovens.
    Coal-to-chemicals
    A group of processes that can convert coal to chemical intermediates, usually products that are substitutable for petrochemical products. These processes typically proceed via synthesis gas (syngas) and involve gasification followed by Fischer-Tropsch synthesis or methanol-to-olefin processes.
    Coal-to-gas
    A process by which mined coal is first turned into synthesis gas or syngas, i.e. a mixture of hydrogen and carbon monoxide. and then into synthetic methane.
    Coal-to-liquids (CTL)
    The transformation of coal into liquid hydrocarbons. This can be achieved through either coal gasification into synthesis gas or syngas, i.e. a mixture of hydrogen and carbon monoxide, combined with Fischer-Tropsch or methanol-to-gasoline synthesis to produce liquid fuels, or through the less developed direct-coal liquefaction technologies in which coal is directly reacted with hydrogen.
    Coal-to-olefin
    One of the coal-to-chemicals routes, targeting short-chain unsaturated alkenes such as ethylene or propylene, which are precursors to polymers and plastics.
    Coalbed methane
    The category of unconventional natural gas that refers to methane found in coal seams.
    Coefficient of performance
    A measure of heat pump (or air conditioner) efficiency. Calculated as the amount of power drawn out of the compressor as heat (or cold) divided by the amount of power supplied to the compressor. A COP of 2 indicates that 2 kW of heat could be supplied for each kW of electricity input. See also seasonal coefficient of performance.
    Cogeneration
    See co-generation.
    Coke dry quenching (CDQ)
    The removal from coke ovens of hot coke at a temperature of approximately 1 000 °C, followed by cooling and keeping it dry with inert gas. Waste heat can be used in a recovery boiler to generate electricity.
    Coke oven coke
    The solid product obtained from the carbonisation of coking coal at high temperature.
    Coking
    In refining, a process by which heavy crude oil fractions can be thermally decomposed under conditions of elevated temperatures and pressure to produce a mixture of lighter oils and petroleum coke. The light oils can be processed further in other refinery units and blended to meet product specifications. The coke can be used either as a fuel or in other applications such as the manufacture of steel or aluminium.
    Coking coal
    A type of coal that can be used for steel making (as a chemical reductant and a source of heat), where it produces coke capable of supporting a blast furnace charge. Coal of this quality is commonly known as metallurgical coal.
    Cold fusion
    A theoretical type of nuclear reaction that would occur at room temperature.
    Colliery gas
    See coalbed methane.
    Combined heat and power (CHP)
    See co-generation.
    Combined-cycle gas turbine (CCGT)
    A type of power plant that operates two thermodynamic cycles: a topping cycle involving a gas turbine; and a bottoming cycle involving a steam turbine that runs on steam raised with high-temperature waste heat from the gas turbine. Usually run on natural gas and generally have a capacity of around 400 MW, but can be optimised for hydrogen. When running on natural gas, sometimes known as NGCCs. At efficiencies of around 60%, a combined-cycle approach is significantly more efficient than a single-cycle plant. Steam turbines are generally around 42-45% efficient, for example. See also OCGT.
    Combustible fuels
    Material that is used to produce heat and power. Includes coal, solid bioenergy, liquid fuels and gaseous fuels.
    Combustible renewables
    Material from renewable sources that is used to produce heat and power. Includes bioenergy and hydrogen-based fuels derived from renewable electricity.
    Combustion
    The primary means of harnessing the chemical energy in combustible fuels. Uses heat or pressure to activate a chemical reaction that releases more energy than used as an input. Combustion can occur in boilers, turbines, engines and other devices. Fuel cells, however, do not operate via combustion but via electrochemical oxidation.
    Committee on Budget and Expenditure
    A committee that forms part of the IEA governance structure. Advises the Governing Board on resource management and administration. In particular, advises the Governing Board on budgetary matters. See also CERT, SEQ, SOM, SLT and SGD. For more information: https://www.iea.org/about/structure.
    Committee on Energy Research and Technology
    A committee that forms part of the IEA governance structure. Convenes government representatives to co-ordinate and promote the development, demonstration and deployment of clean energy technologies. Has established four working parties: the Working Party on Fossil Energy; the Working Party on Renewable Energy Technologies; the Working Party on Energy End-Use Technologies; and the Fusion Power Co-ordinating Committee. Has also established an Experts' Group on R&D Priority-Setting and Evaluation (EGRD) to advise on R&D priority-setting, linkages to governmental policy objectives, methods in the evaluation of R&D activities, and an understanding of emerging R&D topics. See also SEQ, SOM, SLT, SGD and CBE. For more information: https://www.iea.org/about/structure.
    Compact fluorescent lamp (CFL)
    A type of fluorescent lamp designed to fit into standard fittings in buildings and electric goods. In fluorescent lighting, electrons that are bound to mercury atoms are excited to states where they will radiate ultraviolet light as they return to a lower energy level. Emitted ultraviolet light is converted into visible light as it strikes a fluorescent coating on the tube (lamp). More efficient than incandescent lamps but less efficient than light-emitting diodes.
    Complex refinery
    An oil refinery containing upgrading units such as catalytic cracking, hydrocracking or coking, in addition to the units found in a hydroskimming refinery. Has the highest demand for hydrogen.
    Compressed air energy storage (CAES)
    A means of storing electrical energy that involves powering a motorised compressor to compress air into a confined space, such as an underground cavern. Upon release, the compressed gas expands to power a turbine generator that produces electricity. Has the capability to store electricity as potential energy over long durations.
    Compressed natural gas (CNG)
    A means of storing and transporting natural gas in situations where high volumetric energy density is valuable. Used as a fuel in CNG vehicles, where it is stored in high-pressure fuel cylinders. Produces fewer exhaust and greenhouse gas emissions than motor gasoline or diesel oil, but more direct emissions than electric vehicles. Used most frequently in light-duty passenger vehicles and pickup trucks, medium-duty delivery trucks, and in transit and school buses. CNG vehicles can also run on compressed biomethane.
    Concentrating solar heating
    The use of mirrors to increase the amount of solar heat absorbed in a given location by a working fluid that can transfer the heat to a commercial or residential application. Also called concentrated solar heat.
    Concentrating solar power
    Thermal power generation technology that collects and concentrates sunlight to produce high temperature heat to generate electricity.
    Condensates
    Liquid hydrocarbon mixtures recovered from associated or non-associated gas reservoirs. Comprise C5 and higher carbon number hydrocarbons and normally have an API gravity between 50° and 85°.
    Consumption subsidy
    The magnitude, expressed in monetary units, of a government intervention that directly shields an energy consumer from the full cost of supply (or the opportunity cost of unexported energy). For fossil fuels, the IEA uses a so-called "price-gap approach" whereby it establishes a market reference price for different fuels – and for electricity produced from these fuels – and then compares that with the price paid by consumers. Where the end-user price is lower than the reference price, that is counted as a subsidy. See also production subsidy and fossil fuel subsidy.
    Contango
    The oil market is said to be in contango when the price of futures or physicals contracts for near delivery months is at a discount to more distant months. See also: backwardation.
    Contract for difference
    A type of floating (or sliding) feed-in-premium whereby the operator must pay back the difference between the wholesale and guaranteed price if the wholesale price is above the guaranteed price
    Conventional bioenergy
    Bioenergy from food crop inputs that include sugar cane, sugar beet, corn, wheat, oil palm, soya, rapeseed (canola) and sunflower. Also referred to as "first-generation bioenergy".
    Conventional biofuels
    See conventional bioenergy.
    Conventional blendstock for oxygenate blending
    Unfinished gasoline that is made ready to be blended with ethanol. The addition of ethanol reduces knocking and smog formation, but is generally only possible close to the point of sale, which explains why it is a widely traded product. See also reformulated blendstock for oxygenate blending , which is similar but has stricter environmental specifications.
    Conventional liquid biofuels
    Fuels produced from food crop feedstocks. Commonly referred to as first generation biofuels and include sugar cane ethanol, starch-based ethanol, fatty acid methyl ester (FAME) from vegetable oils such as palm, rapeseed or soybean oil, straight vegetable oil (SVO) and hydrotreated vegetable oil (HVO) produced from vegetable oils such as palm, rapeseed or soybean oil.
    Conventional natural gas
    Refers to natural gas extracted using traditional drilling techniques. It includes both onshore and offshore natural gas (including from the Arctic).
    Conventional oil
    Refers to oil extracted using traditional drilling methods. It includes onshore and offshore crude oil (including from the Arctic), enhanced oil recovery, and natural gas liquids produced from conventional gas fields. 
    Conventional oil and gas
    Includes conventional oil and conventional gas
    Conversion/upgrading
    The oil refinery processes of cracking and reforming heavier petroleum fractions to change the molecule size or structure to create compounds with different properties and higher average value.
    Cooling degree day (CDD)
    A measurement to describe the overall need for cooling in buildings. The number of degrees that a day’s average temperature is above a given temperature (normally 18 °C). This temperature is the point above which the consumer is assumed to use energy for space cooling. During the cooling season, warmer-than-normal temperatures tend to lead to increased electricity use, with increased demand for electricity often met by incremental use of oil products and natural gas. See also heating degree day.
    Cost, insurance and freight
    In oil trade, refers to a transaction in which the seller pays to insure and transport the goods to the buyer’s destination port. See also free on board.
    Covering
    In oil trade, the purchase of an opposite futures or paper contract to offset a previously established sale (short position) or purchase (long position).
    Crack/crack spread
    Any of a number of differentials that indicate relative refining profitability. The heat crack is the difference between the price of heating oil and the price of crude, and the gas crack is the difference between the gasoline price and the crude price.
    Cracked residue
    The heavy residual liquid from cracking operations at a refinery or petrochemical plant. See also vacuum residue and atmospheric residue.
    Cracking
    Refinery and petrochemical processes whereby large, heavy, complex hydrocarbon molecules are broken down into simpler and lighter molecules in order to derive a variety of lighter, higher-value products. When this process is brought about by applying heat only, the process is referred to as thermal cracking. If a catalyst is also used, the process is known as catalytic cracking (or fluid catalytic cracking), or hydrocracking if the process is conducted over special catalysts in the presence of hydrogen.
    Critical minerals
    A wide range of minerals and metals that are essential in clean energy technologies and other modern technologies and have supply chains that are vulnerable to disruption. Although the exact definition and criteria differ among countries, critical minerals for clean energy technologies typically include chromium, cobalt, copper, graphite, lithium, manganese, molybdenum, nickel, platinum group metals, zinc, rare earth elements and other commodities.
    Crude distillation unit
    A central processing unit in most oil refineries. Crude oil is fed in and heated to 100-137 °C, which allows salts, which can be harmful and corrosive to some equipment, to be removed. The crude is then heated to up to 400 °C where the vapours and liquids separate according to the different temperatures at which they boil/condense. Lighter fractions such as liquefied petroleum gas are separated first, then gasoline, naphtha, diesel, kerosene, heavy oils and, finally, bitumen and waxes. Also known as the atmospheric distillation unit.
    Crude oil
    The unrefined petroleum oil extracted from geological formations. The most quoted oil prices in economic statistics refer to the traded prices of standard barrels of crude oil. In IEA statistics it includes crude oil, natural gas liquids, refinery feedstocks, additives, and other hydrocarbons. In Energy Data Centre statistics, crude oil does not include natural gas liquids, refinery feedstocks, additives or other hydrocarbons.
    Crush spread
    In oil trade, the price differential or profit margin between the price of a liquid biofuel feedstock and its end product (e.g. the spread between corn and bioethanol prices).
    Cyclic steam stimulation
    A method of recovering bitumen and heavy oils from geological hydrocarbon reservoirs. Steam is injected into a well at a high temperature (300-340 °C) for an extended period of time (typically weeks or months) to liquefy the bitumen until it can be pumped out. When the production of oil decreases, the cycle is repeated. May recover 20-25% of oil in the formation, but the cost of injecting steam is high. Also called "huff-and-puff" operation.

  • D

    Darcy (darcy)
    A unit of permeability, used in petroleum engineering, CO2 storage and geothermal.
    Daylighting
    See passive solar energy.
    Days of forward demand
    In the oil sector, calculated on the basis of the average daily demand for the next three months. Stock comparisons with previous years are made in volume terms and days of forward demand. Comparisons in absolute terms effectively understate the differences since they ignore any growth in demand, which increases operating minima, while comparisons in days of forward demand tend to overstate the differences since operating minima increase by less in percentage terms than the growth in demand. They also depend on the accuracy of the demand forecast.
    Deadweight tons
    A measure, in long tons, of a tanker’s total capacity to carry cargo, bunkers, water, stores and people. In oil trade, a tanker’s capacity to carry crude or product cargo, in metric tonnes, is slightly less than its deadweight.
    Decline rate
    The annual rate, in per cent per year, at which oil production declines in a reservoir. As fluids are produced from a subsurface reservoir, the pressure of the remaining fluids decreases. Generally speaking, oil production will tend to enter natural decline once around 50% of the oil in the reservoir has been produced. Natural reservoir decline can be distinguished from managed decline, whereby efforts are made to sustain reservoir pressure and to enhance total oil recovery. Individual fields can therefore have multiple production peaks.
    Deliveries
    The supply of goods, such as oil products, from primary stocks to wholesalers and retailers or direct to end users.
    Delivery month
    The month specified in a given physicals or futures contract for delivery of the physical commodity, such as crude oil or cash.
    Demand
    In economics, the amount of a good or service that consumers are willing to buy at a particular price. In energy, it is generally understood to be the quantity of energy products that are expected to be consumed by all users at prevailing prices. Typically, total demand for an energy product includes uses as final energy products as well as uses for transformation (to electricity, hydrogen or other fuels), losses in transmission and distribution, and non-energy uses.
    In IEA statistics, oil demand is total inland deliveries plus refinery fuels and bunkers minus backflows from the petrochemical sector. It is thus equivalent to oil consumption plus any secondary and tertiary stock increases.
    Demand pull
    A type of government policy that aims to increase the deployment of a selected technology by increasing demand for its services, thus indirectly raising production of the technology and decreasing prices through economies of scale and induced innovation. Demand pull policies can include purchase incentives, performance-based payments (such as auctions for long-term contracts or contracts for difference), investment in supporting infrastructure, public procurement, obligations or standards. Sometimes used to refer to policies that specifically target induced innovation via market forces in a given technology area, an approach referred to in IEA analysis as "market pull". Often contrasted with "technology push" measures. The term may also be applied to all factors that generate induced innovation, not just government policy.
    Demand response (DR)
    Shifting or shedding electricity demand to provide flexibility in wholesale and ancillary power markets, helping to balance the grid. Shifting means moving the load curve in time (without affecting total electricity demand). Shedding means interrupting demand for a short duration or adjusting the intensity of demand for a certain amount of time (which can affect total demand). Usually driven by one of two mechanisms: price-based programmes (or implicit demand response), which use price signals and tariffs to incentivise consumers to shift consumption, and incentive-based programmes (or explicit demand response), which monetise flexibility through direct payments to consumers who shift demand in a demand-side response programme. Aggregators of demand response into MW-scale quantities for trading are sometimes called virtual power plants (VPPs).
    Demand-side response
    Describes actions which can influence the load profile such as shifting the load curve in time without affecting total electricity demand, or load shedding such as interrupting demand for a short duration or adjusting the intensity of demand for a certain amount of time.
    Demonstration project
    A new technology introduced to a given market at the size of a single full-scale commercial unit. The purpose is to show that the technology is effective and to reduce the perception of risk for financiers.
    Derivatives
    A contract that derives its value from the performance of an underlying entity, such as an asset, index or interest rate. Can be used for a number of purposes, including insuring against price movements (hedging), increasing exposure to price movements for speculation, or gaining access to otherwise hard-to-trade assets or markets. In energy trade, generally used as a financial instrument to hedge risk, but can also be used for speculative purposes.
    Development well
    A well drilled in an area that has already been proved to contain oil.
    Diesel
    An oil product, typically the output of a refinery, designed to match the requirements of a diesel engine. Can also be produced synthetically from synthesis gas (syngas). Generally composed of about 75% saturated hydrocarbons and 25% aromatic hydrocarbons, with an average chemical formula of C12H23. The quality of diesel combustion is indicated by the cetane number. In advanced economies, diesel fuel is now of the ultra-low sulphur diesel (ULSD) type. Diesel has a specific energy of around 45.5 MJ/kg and contains the energy of 1.077 litres of gasoline equivalent (lge).
    Direct air capture
    The capture of CO2 from the atmosphere in a form that is compatible with permanent storage in deep geological formations or use in the production of fuels, chemicals, building materials or other products. When coupled with permanent CO2 storage, a carbon removal technology (CRT) that can help balance emissions elsewhere in the economy in the achievement of net zero emissions or even net negative emissions.
    Direct current (DC)
    An electric current that is unidirectional (the flow of charge is always in the same direction) and the amperage does not change. Different from alternating current (AC) in which the direction changes regularly. DC electricity is produced by solar photovoltaics and batteries, and is used in many household electronics. It is also use in high-voltage direct current (HVDC) cables for long-distance transmission that is more efficient than using AC, including for undersea interconnectors. To switch from DC to AC, for example when connecting a solar plant to the grid, an inverter is required. To switch from AC to DC, for example when charging household electronics, a rectifier is used.
    Direct injection coal engine (DICE)
    A modified diesel engine running on a slurry of ground coal (or solid bioenergy) and water. Known as micronised refined carbon (MRC). Plant efficiency can reach around 40%.
    Dirty cargoes
    In oil trade, comprise crude oil or heavy, viscous petroleum products (heavy fuel oil, for example, which coats the sides of the cargo tanks). Vessels carrying dirty cargoes may be referred to as dirty vessels.
    Discovered
    Where the potential for CO2 storage within a specific subsurface formation has been quantified, storage resources are classified as discovered.
    Discretionary stocks
    Oil stocks available to industry to use as and when it pleases. Discretionary stocks typically only represent 10% of total industry stocks. Often used with financial instruments as an investment.
    Dish/Stirling technology
    See parabolic dish concentrators.
    Dispatchable generation
    Electricity from technologies whose power output can be readily controlled, i.e. increased to maximum rated capacity or decreased to zero, in order to match supply with demand. Includes coal-fired plants, gas-fired plants, biomass-fired plants, batteries (and other forms of storage), hydropower, geothermal power, nuclear (depending on the operating parameters) and hydrogen-fired plants. Dispatchable low-carbon generation includes biomass-fired plants, batteries (and other forms of storage), hydropower, geothermal power, nuclear, hydrogen-powered plants and natural gas-and coal-fired plants equipped with a high level of carbon capture with CO2 storage.
    Dispatchable power generation
    See dispatchable generation.
    Disposable plastic
    See single-use plastic.
    Distillation
    The first stage in the refining process of separating crude oil components at atmospheric pressure by the heating, and subsequent condensing, of the fractions (unfinished petroleum products) by cooling.
    Distributed energy resources (DER)
    Small-scale energy resources usually situated near sites of electricity use, such as rooftop solar panels and battery storage. There is no single definition, however, so classifications vary depending on who is using the term, for what purpose and in what context. Definitions also differ in the extent to which they include resources on both sides of the meter, and whether they include energy efficiency. If situated on the grid side of the meter, they are usually connected to the distribution grid, not the transmission grid.
    Distributed generation (DG)
    See distributed energy resources
    Distribution grid
    See distribution system.
    Distribution network
    See distribution system.
    Distribution system
    In energy supply via fixed network infrastructure, the distribution system is the stage that connects to homes, industry and other end users. In gas supply, the distribution network is at a lower pressure (up to 2 bar or 200 kPa) than the transmission network (up to 70 bar or 7 MPa). In electricity supply, the distribution network is at a lower voltage (up to 50 kV) than the transmission network (up to 1 000 kV or more). See also transmission system.
    Distribution system operator
    An entity responsible for distributing energy to the final consumers and managing energy at this level of the grid. As with transmission system operators, generally either state-owned or granted a licence as a network monopoly for a fixed period under a regulatory contract to provide a service and be remunerated by fees claimed via energy bills.
    District heating
    Provision of hot water or steam to customers via an insulated pipe network. District heat is supplied from co-generation facilities, heat generators (including heat pumps and boilers), waste heat recovery from industrial sources or waste heat from primary-function electricity generators. The working fluid in the district heat network provides a source of thermal storage. District heat networks are most commonly found in urban areas or industrial parks with a high density of customers and are generally more energy efficient than a counterfactual in which each customer generates their own heat. Modern district heat networks are able to operate at lower temperatures to improve efficiency and include thermal storage technologies (in addition to linepack).
    Double flash cycle
    A type of power generation system used for geothermal electricity generation that is generally used for geothermal fluid temperatures higher than 250 °C. Similar to a flash cycle, but employs a separator before the flasher to create high-pressure and low-pressure streams of steam. The high-pressure fluid is sent to the high-pressure inlet of the turbine and the lower-pressure steam is sent to the low-pressure inlet of the same turbine. In this way, more power can be extracted from a geothermal source.
    Downstream
    In energy supply, the stage of the supply chain that delivers energy products to final consumers. In the oil industry, it includes refining of crude oil into petroleum products, and the shipping, distribution and marketing of these products. Downstream connects to midstream (shipping and transport of crude oil or other unrefined energy products), which connects to upstream (exploration and extraction). See also upstream and midstream.
    Dry steam
    A type of power generation system used in geothermal power plants, in particular where the temperatures are above 150 °C. Dry steam geothermal systems were the earliest type of geothermal power plant and use steam emanating directly from underground, rather than flash cycles that convert high pressure water to steam to increase efficiency.
    Dual fuel vehicle
    A vehicle that is capable of using two types of fuel at the same time in a mixture.

  • E

    E10
    A blend of liquid biofuels and conventional fuels, with the biofuel component being 10% bioethanol by volume in gasoline. Other blends may be E5, E15, E20, E85.
    E15
    A blend of liquid biofuels and conventional fuels, with the biofuel component being 15% bioethanol by volume in gasoline. Other blends may be E5, E10, E20, E85.
    E20
    A blend of liquid biofuels and conventional fuels, with the biofuel component being 20% bioethanol by volume in gasoline. Other blends may be E5, E10, E15, E85.
    E5
    A blend of liquid biofuels and conventional fuels, with the biofuel component being 5% bioethanol by volume in gasoline. Other blends may be E10, E15, E20, E85.
    E85
    A blend of liquid biofuels and conventional fuels, with the biofuel component being 65% to 85% bioethanol by volume in gasoline. Other blends may be E5, E10, E15, E20.
    Economies of scale
    Cost advantages reaped in manufacturing and installation when fixed and variable costs rise more slowly than the number of units of output. It is associated with mass production of similar goods, as well as the use of larger equipment, such as pipelines for which material needs do not scale linearly with throughput. Though much rarer, diseconomies of scale have also been seen.
    Economies of scope
    Economic savings that are gained by producing two or more distinct goods together because the cost of doing so is less than that of producing each separately. Economies of scope apply when by-products are marketed or a manufacturer enters new business areas.
    Electric power
    Technically, the rate at which electrical energy is transferred by an electric circuit, measured in watts. However, it is commonly used as a synonym for electricity. In IEA analysis, the term "power plant" is inclusive of plants that also produce heat.
    Electric vehicle (EV)
    Electric vehicles comprise of battery electric vehicles (BEVs) and plugin hybrid electric vehicles (PHEVs). See also battery electric vehicle (BEV) and plug-in hybrid electric vehicle (PHEV).
    Electrical capacity
    A term usually applied to the maximum output that an electricity generator can physically produce (or accept, in the case of an electricity storage device), measured in watts (W). Often referred to as the nameplate capacity, a value ascribed to the facility at the time of installation. For electricity storage devices, the capacity (in W) should not be confused with its capacity to hold energy (denoted in watt hours [Wh], e.g. a 1 MW battery system that can run at full output for four hours would have an energy capacity of 4 MWh).
    Electricity
    A means of transferring energy from one place to another, generally in a form that is more useful for converting energy into services such as lighting, heating or transport. The means of moving electricity is usually an electric circuit in which an electric charge is made to flow along a closed path, for example within a cable. Use of electricity by consumers to provide energy services does not create greenhouse gas emissions or air pollution at the point of use, although the generation of the electricity may do so.
    Electricity and heat generation
    Includes electricity generation, heat generation and co-generation.
    Electrolyser
    A device that uses direct electrical current to drive an otherwise non-spontaneous chemical reaction. Commonly used in the production of chemicals such as chlorine. Water electrolysers split water into hydrogen and oxygen, for the production of hydrogen, and are increasingly being applied to energy challenges such as the conversion of CO2 to useful products and the reduction of iron ore.
    Emerging market and developing economy (EMDE)
    All other countries not included in the advanced economy regional grouping.
    Emission factor
    A measure of the expected greenhouse gas emissions resulting from the combustion of one unit of a given fuel or from the production of one unit of a given source of electricity (or other secondary energy carrier). Also used to refer to the weighted average emissions associated with the production of electricity from a range of sources. Usually expressed as mass of CO2 equivalent per kWh or per volume of natural gas.
    Energy access
    A household having reliable and affordable access to both clean cooking facilities and to electricity, which is enough to supply a basic bundle of energy services initially, and then an increasing level of electricity over time to reach the regional average.
    Energy efficiency
    The ratio of the quantity of useful work performed relative to the quantity of energy consumed. Something is more energy efficient if it delivers more services for the same energy input, or the same services for less energy input. For example, when a compact florescent light (CFL) bulb uses less energy than an incandescent bulb to produce the same amount of light, the CFL is considered to be more energy efficient.
    Energy efficiency indicator
    Helps demonstrate whether one thing is more energy efficient than another. Can be highly aggregated (for instance, energy consumption per appliance for all appliances) or disaggregated (for instance, average heating consumption per unit of floor area of single houses using natural gas for heating). Usually comprise energy consumption as numerator and activity data as denominator. There are some exceptions, such as the “energy” consumption of cars, which can be expressed in volume (litres) or distance (miles) and not converted into energy units. 
    Energy intensity
    A measure of the energy used to provide a standardised product or service. Also used to normalise and compare energy consumption between economies by expressing energy consumption per unit of GDP, e.g. MJ per USD.
    Energy investment
    In IEA analysis, defined as the ongoing capital spend on assets for the production, transformation, transport and consumption of energy. For more information, see the methodological annexes of the IEA World Energy Investment reports. Clean energy investment is a subset of energy investment.
    Energy mix
    The variety of energy sources used to satisfy demand for energy services in a country or region. Expressed in terms of the share of total energy supply or final consumption represented by each source.
    Energy poverty
    A lack of energy access. Different definitions exist depending on differing national contexts. For example, the European Commission defines energy poverty as a household spending a high percentage of its income on energy bills, or reducing its energy consumption to a degree that negatively affects its health and well-being.
    Energy security
    The uninterrupted availability of energy sources at an affordable price.
    Energy service
    A personal or societal gain from the use of energy, the ultimate purpose of an activity that consumes energy. Includes (inter alia) heating, cooling, lighting, entertainment, mobility, nourishment, hygiene and education. An important concept in energy efficiency, whose objective is to provide an equal or greater level of energy service with fewer energy inputs. While sometimes difficult to measure, it is conceptually important to distinguish this goal from narrower attempts to improve the energy efficiency of a subset of ways to provide the energy service, such as via a personal vehicle or individual heater. See also energy efficiency indicators.
    Energy service company
    A type of customer-facing organisation that delivers energy efficiency projects to energy consumers, with each project’s financing relying on the value of the resulting energy savings. The contractual relationship is sometimes based on the provision of "energy services" (heating, cooling, ventilation, light etc.) for a given price, rather than units of energy (electricity, gas etc.).
    Energy sources
    All types of energy supply, including: all solid, liquid and gaseous fuels; electricity; uranium; steam and hot water; and the traditional fuels such as fuelwood, charcoal, vegetal and animal wastes.
    Engineered geothermal systems
    See enhanced geothermal system.
    Enhanced geothermal system (EGS)
    A technique for harnessing geothermal energy that relies on improving the natural permeability of rock, for example by creating a subsurface fracture system into which water can be pumped through injection wells. Fluid is typically injected into the subsurface under carefully controlled conditions, which causes pre-existing fractures to reopen, creating permeability. Subsequently, injected water is heated by contact with the rock and returns to the surface through production wells. As of 2023, a handful of EGS projects have been undertaken, but no commercial-scale facilities are in operation as yet. Also called engineered geothermal systems or stimulated geothermal systems (SGS).
    Enhanced oil recovery (EOR)
    Oil produced after primary recovery and secondary recovery (using water injection). Various technologies exist, such as steam injection, hydrocarbon injection, underground combustion and CO2 flooding (known as CO2-EOR). Also known as tertiary oil recovery.
    Ethane
    A naturally gaseous straight-chain hydrocarbon (C2H6).
    Ethanol
    An alcohol with broad application in the chemical sector and as a fuel additive. When produced from bioresources it is known as bioethanol, which has applications as biogasoline (a liquid fuel) and as a biochemical.
    European seasonal coefficient of performance
    A calculation method for seasonal coefficient of performance that is used in European Union legislation.
    European seasonal energy efficiency ratio
    A calculation method for seasonal energy efficiency ratio that is used in European Union legislation.
    Ex-tax price
    The price before taxes are levied.
    Expiry date
    In oil trade, the final day on which futures trading in a particular month is permissible. Any contracts left open following this day must be settled by delivery or cash settlement.
    Exploration
    In the oil and gas industry, the process of searching for underground accumulations of oil and natural gas that can be economically produced. One of the activities of "upstream" oil and gas, along with production, which is the stage focused on retrieving trapped oil and gas resources that have been discovered. The same terminology can be applied to searching for geothermal energy and CO2 storage resources.
    Exports
    In IEA statistics, goods having crossed national territorial boundaries whether or not customs clearance has taken place. For coal, exports comprise the amount of fuel supplied to other countries, whether or not there is an economic or customs union between the relevant countries. Coal in transit is not included. For oil, quantities of crude oil and oil products exported under processing agreements (i.e. refining on account) are included. Re-exports of oil imported for processing within bonded areas are shown as an export of product from the processing country to the final destination. For natural gas, imported LNG that is exported to another country after regasification is considered both as an import and an export of gas. For electricity, amounts are considered as exported when they have crossed national territorial boundaries. If electricity is “wheeled” or transited through a country, the amount is shown as both an import and an export. In IEA analysis, import–export balances are typically reported on a net trade basis.
    Extra-heavy oil
    The portion of heavy oil having an API gravity of less than 10°. The largest extra-heavy oil accumulation is the Venezuelan Orinoco belt, which contains around 90% of the world's extra-heavy oil when measured on an in-place basis.
    Extra-heavy oil and bitumen
    Includes extra-heavy oil and oil sands.
    Extraction
    See production.

  • F

    Fast-breeder reactor
    A nuclear fission reactor in which the free neutrons have kinetic energy exceeding 1 MeV (100 TJ/kg), giving a speed of over 14 000 km per second. While fed with similar uranium fuels to other fission reactors, fast-breeder reactors generate more fissile material than they consume. They produce less of certain types of nuclear waste and require less fuel than other fission reactors, which raised interest in them in the 1960s and 1990s due to concerns about uranium resources and waste generation, respectively. As of 2023, all large-scale fast-breeder reactor power stations are liquid metal fast-breeder reactors (LMFBR) cooled by liquid sodium. Two plants larger than 100 MW are operational in Russia, and one is under development in each of India and China.
    Fatty acid methyl ester
    A type of liquid biofuel that can be used in diesel engines. Derived by the transesterification of fats, such as recycled vegetable oil, soybean oil, rapeseed oil, sunflower oil, jatropha oil and palm oil. The process requires a methanol input. As of 2023, this methanol is usually derived from a fossil fuel source, but it is possible to use a renewable source of methanol to produce a liquid biofuel with a higher renewable content. Higher-performing liquid biofuels produced by the hydrogenation of fats (rather than transesterification) are known as hydrotreated vegetable oil.
    Feed-in premium
    A type of support policy based on performance-based payments and typically available to producers of energy products with certain specified environmental credentials, such as renewable electricity. The difference between a feed-in-premium and a feed-in-tariff is that a feed-in-premium is paid as a sum on top of the wholesale price. This sum can be "fixed" or "floating" (or "sliding"). A fixed feed-in-premium is a defined amount for each unit of energy produced. A floating feed-in-premium is a variable top-up between the average wholesale price and a previously defined guaranteed price. The longer the period over which the averaging occurs, the more the operator is exposed to market risk. A contract for difference is a specific type of floating feed-in-premium whereby the operator must pay back the difference between the wholesale and guaranteed prices if the wholesale price is above the guaranteed price.
    Feed-in tariff
    A policy measure that guarantees a level of remuneration, usually above market rates, to energy producers for each unit of output. Used to encourage investment in renewable electricity plants and bioenergy plants by reducing price and demand risk. In some jurisdictions, different technology types have been offered different levels of remuneration within the same feed-in tariff system. As renewable electricity costs have declined and technology and other perceived risks have receded, feed-in tariffs for the more mature technology types have largely been superseded by contracts linked to market prices. Feed-in tariffs are a type of performance-based payment policy. The first feed-in tariff was established by the 1978 US National Energy Act.
    Feedstock
    A physical input into an industrial process, such as chemical production or biorefining. In energy analysis, feedstock typically refers to one of three things: energy products used as reactants in the chemical sector (i.e. non-energy use), especially refined oil products and natural gas for petrochemicals; carbon and hydrogen inputs to synthetic fuel production, including CO2 captured from the atmosphere; and bioenergy inputs to gaseous and liquid biofuel production, including energy crops and biological waste.
    Final investment decision
    A key point in the development of a project, such as a major energy asset, at which the decision to proceed is made with financial commitment to construction or ownership. Usually taken soon after financial close, the point at which a complete financing package is put together. In IEA analysis, typically taken to be the moment at which the construction of an energy project begins. It is a leading indicator of energy investment and change in the stock of energy-related assets.
    First month/front month
    In oil trade, the futures contract month closest to expiry.
    First-generation biofuels
    See conventional bioenergy.
    Fischer-Tropsch synthesis
    Catalytic process to produce synthetic fuels, e.g. diesel, kerosene or naphtha, typically from mixtures of carbon monoxide and hydrogen (synthesis gas or syngas). The inputs to Fischer-Tropsch synthesis can be from biomass, coal, natural gas, or hydrogen and CO2.
    Fission
    See nuclear fission
    Fixed offshore wind
    A type of offshore wind electricity generator that is fixed to the seabed.
    Flag
    In seaborne energy trade, refers to the country under whose maritime regulatory system a vessel is registered.
    Flare
    A device for burning produced hydrocarbons that an operator decides not to sell or reinject. A source of CO2 and methane emissions, but preferable to direct release of the methane gas to the atmosphere in terms of climate impact. Flares can be installed at oil and gas production sites where gas production exceeds on-site demand or nearby pipeline capacity, to combust methane emissions. Portable flares can expand a facility’s flare capacity and provide an outlet for gas captured during well workovers or completions.
    Flaring
    The burning off of gas produced in association with oil or natural gas extraction that, for technical or economic reasons, the operator has decided not to capture for reinjection or shipment. A source of greenhouse gas emissions. See also venting.
    Flash cycle
    A type of power generation system used in geothermal power plants, in particular where temperatures are between 180 °C and 250 °C. High-pressure hot water from underground is converted to steam in a "flasher", and is separated from the remaining water and used to run a turbine. While some early "dry steam" geothermal systems used steam emanating directly from underground, flash cycles have become more common. However, more efficient systems such as double flash cycles and binary cycles are increasingly used.
    Flex-fuel vehicle (FFV)
    A vehicle (typically a road vehicle) that has one drivetrain but can accommodate different types of fuels in the same tank in any (or a wide range of) mixtures. A common example is a gasoline and bioethanol flex-fuel vehicle.
    Floating liquefied natural gas
    A barge-mounted terminal for liquefying and storing natural gas as liquefied natural gas. The first plant started operation in 2016.
    Floating offshore wind
    A type of offshore wind electricity generator that is not fixed to the seabed, thereby allowing wind generation in deeper waters.
    Floating production, storage and off-loading vessel
    A vessel used offshore as a floating platform for the drilling, production, storage and loading of crude oil. Often converted tankers.
    Floating storage
    See floating storage/oil in transit
    Floating storage regasification unit
    Ship-mounted terminals for storing and regasifying liquefied natural gas. Seaborne and can be moved to where they are needed.
    Floating storage/oil in transit
    In energy statistics, estimates of the change in global crude oil stocks in transit at sea between producing and consuming countries or held in moored tankers used for temporary storage.
    Flue gas desulphurisation (FGS)
    Processes for the reduction of sulphur dioxide (SO2) emissions from the combustion of sulphur-containing fuels. Generally associated with five methods used at coal-fired power plants: wet scrubbing; spray-dry scrubbing; wet sulphuric acid process; SNOX; and dry sorbent injection. Depending on the process, modern systems may reduce power plant efficiency by as little as 2 percentage points. May remove more than 90% of the SO2 in the flue gases; its use has reduced the incidence of acid rain.
    Fluorescent lamp
    A lamp that produces light using fluorescence, usually via low-pressure mercury-vapour gas-discharge produced by an electric current. Larger lamps are straight tubes sometimes called strip lights. Smaller lamps use curved tubes, generally called compact fluorescent lamps. While more efficient than incandescent lamps, fluorescent lamps have around half the efficiency of light-emitting diodes, which do not contain mercury.
    Fluorescent lighting
    See fluorescent lamp.
    Forgetting-by-not-doing
    Interruptions in production or use of a technology that cause accumulated knowledge to be lost and lead to higher unit costs for the next unit put into service after the interruption.
    Fossil fuel subsidy
    A government intervention that has the impact of reducing the marketed price of a fossil fuel or increasing the profitability of selling a fossil fuel, either directly or indirectly. Includes consumption subsidy and production subsidy. Attempts have also been made to include estimates of non-internalised environmental harms, such as costs of climate change.
    Fossil fuels
    Energy sources that are typically extracted from underground and which have been formed from the fossilised remains of dead plants by exposure to heat and pressure in the Earth's crust over millions of years. Fossil fuels generate greenhouse gases during their extraction, transport and combustion or oxidation. Includes coal, natural gas, oil and peat.
    Fossil fuels with CCUS
    Fossil fuels used for energy purposes with carbon capture, utilisation and storage (CCUS). In IEA analysis, total fossil fuel use is equal to unabated fossil fuels plus fossil fuels with CCUS plus non-energy use of fossil fuels.
    Fracking
    See fracturing.
    Fracturing
    A means of increasing production from low-permeability geological structures by breaking up the rock and expanding fissures, for example by applying very high fluid pressures (hydraulic fracturing). A core technique for the production of unconventional hydrocarbons from shale formations, such as tight oil and gas. Can also be applied to geothermal and other subsurface energy processes.
    Free on board
    A transaction whereby the seller makes a commodity, such as coal or crude oil, available at a given price at an agreed time and location. It is the responsibility of the buyer, not the seller, to arrange and pay for transport and insurance to move the commodity to its final destination. See also cost, insurance and freight.
    Freight rate
    See charter rate.
    Fuel cell
    An electrochemical device for generating electricity that uses electrolysis to convert chemical energy in a fuel to electrical energy. Fuel cells have been developed that can run on hydrogen, natural gas, methanol, formic acid and other fuels. If the fuel is low-emissions hydrogen, the only resulting product from these reactions is water, making it one of the possible means of generating stationary power or onboard power (e.g. in a fuel cell electric vehicle) in a net zero emissions society. Fuel cells can also be optimised for the co-generation of heat and power, and have been used in buildings-scale micro co-generation systems. Some fuel cells are reversible, which means that they can also operate as water electrolysers that produce hydrogen from electricity. Fuel cell types include proton exchange membrane, solid oxide and molten carbonate.
    Fuel cell electric vehicle (FCEV)
    A vehicle (typically a road vehicle) powered by an electric motor for which the electricity is provided by an onboard fuel cell. In most configurations the fuel cell is powered by hydrogen stored onboard, which can provide a low-emissions mode of transport if the hydrogen is low-emissions hydrogen.
    Fuel economy
    Fuel consumption per unit of service provided. Most commonly used as a measure of vehicle efficiency and reported in litres of gasoline equivalent (lge) per 100 km. The fuel economy of a vehicle may be reported based on different driving cycles depending on the region where it is certified or approved for sale. The IEA reports fuel economy values according to the Worldwide Harmonized Light-Duty Test Cycle (WLTC) using, where necessary, simulation-based and measurement-based driving cycle conversion factors. See also: Global Fuel Economy Initiative.
    Fuel oil
    All residual (heavy) fuel oils (including those obtained by blending). Kinematic viscosity is above 10 cSt at 80 °C. Flash point is above 50 °C. Density is above 0.90 kg/l. Heavy fuel oils are referred to as low-sulphur fuel oil (LSFO) if their sulphur content is below 1%. Fuel oil is used mostly in shipping, heating buildings and power generation.
    Fuelwood
    A type of bioenergy resource that usually refers to "roundwood" cut into logs and split before use. In energy statistics, more processed forms of fuelwood – such as wood chips, sawdust and pelletised wood are treated separately.
    Fugitive methane emissions
    Occur from leakages that are not intended, for example because of a faulty seal or leaking valve. See also: methane emissions, vented methane emissions and incomplete flaring methane emissions.
    Fundamentals
    Factors other than psychological or technical that influence price development on the physical or futures market (e.g. physical supply and demand, stock levels, currency exchange rates, interest rates, weather [forecasts] etc.). See also technicals).
    Fusion
    See nuclear fusion.

  • G

    Gas
    See gaseous fuels.
    Gas coke
    A by-product from the carbonisation of bituminous coal for the manufacture of “gas works gas”.
    Gas crack
    The difference between the price of gasoline and the price of crude oil.
    Gas field
    An area of accumulation of pressurised natural gas underground in multiple (potentially linked) reservoirs, trapped by impermeable rock formations. In the energy industry, applied to areas worthy of commercial attention. Natural gas fields are typically deeper than oil fields. Gas fields may also contain crude oil and be referred to as "oil and gas fields".
    Gas fields
    See oil and gas fields.
    Gas processing plant
    See gas treatment.
    Gas storage capacity
    The amount of gaseous fuel, such as natural gas, that can be stored in a given storage facility or across multiple such facilities, typically expressed in terms of the volume that can be injected and withdrawn. Large-scale underground gas storage facilities can include salt caverns, hard-rock caverns, depleted gas reservoirs and depleted aquifers. Above-ground storage can be in tanks for liquefied or gaseous fuels, including storage on maritime vessels and the large gasholder or gasometer stores commonly used for town gas in the 19th century in some countries. As storage in depleted hydrocarbon reservoirs and aquifers always includes some gaseous fuel that is unrecoverable (it is permanently embedded in the geological formation), the capacity of a storage facility normally refers to its working gas capacity not total capacity. The amount of gaseous fuel that is available at a given time is limited by the maximum rate of withdrawal (a function of porosity, valves and pressure, which is in turn related to the level of gaseous fuel inside the store).
    Gas sweetening
    See gas treatment.
    Gas treatment
    A set of processes for the removal of impurities in natural gas, situated between a natural gas well and the entry point into a pipeline system or liquefaction terminal. Gas treatment, or gas processing, includes "gas sweetening" or "acid gas removal", by which sulphur dioxide, CO2 and organic sulphurs are removed to meet pipeline or liquefied natural gas specifications. Large-scale CO2 capture at gas treatment plants has been in operation since the 1970s for enhanced oil recovery.
    Gas treatment plant
    A set of facilities for gas treatment.
    Gas well
    A drilled hole in the earth for the primary purpose of extracting natural gas. See also oil well.
    Gas works
    Plants that manufacture gaseous fuels from solid fuels, such as coal, for distribution to the public either directly or after blending with natural gas.
    Gas-cooled reactor
    A type of nuclear fission reactor that uses a graphite moderator and a carbon dioxide or helium coolant. Includes Magnox, advanced gas-cooled reactors and UNGG reactors. As of 2020, gas-cooled reactors with a total capacity of 7.7 GW were in operation, 2% of global fission reactors.
    Gas-to-liquids (GTL)
    A collective term for processes that convert natural gas to liquid fuels. Typically features the reaction of methane with oxygen or steam to produce synthesis gas (syngas) followed by Fischer-Tropsch synthesis. The process is similar to that used in coal-to-liquids.
    Gas/diesel oil
    See diesel.
    Gaseous fuels
    Fuels in gaseous form including natural gas, biogas, biomethane, hydrogen and synthetic methane.
    Gases
    See gaseous fuels.
    Gasoil
    Medium distillate hydrocarbons, including diesel and light heating oil (distilling between 180 °C and 380 °C), heavy gasoils (distilling between 380 °C and 540 °C) and other gasoils.
    Gasoline
    Complex mixtures of volatile hydrocarbons distilling between approximately 25 °C and 220 °C and consisting of compounds in the C4 to C12 range.
    Gasoline gallon equivalent
    See litre of gasoline equivalent.
    Gasoline-type jet fuel
    Light hydrocarbons for use in aviation turbine power units, distilling between 100 °C and 250 °C. Obtained by blending kerosene and gasoline or naphtha in such a way that the aromatic content does not exceed 25% by volume, and the vapour pressure is between 13.7 kPa and 20.6 kPa.
    Geopressurised
    Oil and gas reservoir fluid pressure that significantly exceeds hydrostatic pressure, possibly approaching overburden pressure. Also used to identify geothermal energy resources, as geopressurised reservoirs are very hot.
    Geothermal
    See geothermal energy.
    Geothermal energy
    Heat derived from the subsurface of the earth, usually using a working fluid such as water to bring the energy to the surface. Can be used for heating and cooling purposes or to generate renewable electricity if the temperature is adequate. Includes hydrothermal, geopressurised, hot dry rock, magma, direct dry steam, flash cycle, double flash cycle, binary cycle and enhanced geothermal systems and shallower ground-source heap pumps.
    Geothermal heat pump
    See ground-source heat pump
    Global average surface temperature
    See global mean surface temperature.
    Global Fuel Economy Initiative (GFEI)
    A global partnership of expert groups that supports governments around the world to set policies for cleaner and more efficient vehicles. The IEA is one of six international partners. GFEI publishes a biannual benchmarking report on the fuel economy of light-duty vehicle sales See: https://www.globalfueleconomy.org.
    Global mean surface temperature
    The mean average of near-surface air temperature over land and sea.
    Global surface temperature
    See global mean surface temperature.
    Global warming
    See climate change.
    Global warming potential
    An index to measure how much infrared thermal radiation a greenhouse gas would absorb over a given time frame after it has been emitted to the atmosphere. Allows the comparison of greenhouse gases’ effectiveness in causing radiative forcing. Expressed as a multiple of the radiation that would be absorbed by the same mass of added CO2, which is taken as a reference gas. Therefore, the GWP of CO2 is 1. For other gases it depends on how strongly the gas absorbs infrared thermal radiation, how quickly the gas leaves the atmosphere, and the time frame being considered.
    Government-controlled stocks
    Primary stocks of energy, exclusively for emergency purposes, owned by governments and organisations that have been established to hold stocks (stock-holding organisations).
    Gravimetric energy density
    See specific energy.
    Green coke
    Green coke (raw coke) is the primary solid carbonisation product from high-boiling hydrocarbon fractions obtained at temperatures below 630 °C. It contains 4-15% by weight of matter that can be released as volatiles during subsequent heat treatment at temperatures up to approximately 1 330 °C.
    Green diesel
    See hydrotreated vegetable oil.
    Greenhouse effect
    The process of greenhouse gases in the earth’s atmosphere trapping some of the heat radiated from the earth’s surface, raising its temperature. This process happens because the sun emits shortwave radiation that passes through greenhouse gases, but the earth emits longwave radiation that is partly absorbed by greenhouse gases. Slight changes in the levels of greenhouse gases in the atmosphere, including water vapour, can cause large changes in atmospheric temperature.
    Greenhouse gas (GHG)
    A gas that exacerbates the greenhouse effect. Includes carbon dioxide (CO2); methane (CH4); nitrous oxide (N2O); hydrofluorocarbons (HFCs); perfluorocarbons (PFCs); and sulphur hexafluoride (SF6).
    Gross calorific value
    The gross calorific value (GCV), or high heat value, measures the total (maximum) amount of heat that is produced by combustion. However, part of this heat will be locked up in the latent heat of evaporation of any water present in the fuel before combustion (moisture), or generated in the combustion process. The latter comes from the combination of hydrogen present in the fuel with the oxidant oxygen (O2) present in the air to form H2O. This combination itself releases heat, but this heat is partly used in the evaporation of the generated water.
    Gross inland energy consumption
    The overall supply of energy (excluding international maritime bunkers) for all activities in the territory of the country.
    Gross input to atmospheric crude oil distillation units
    In energy statistics, this is the total input to atmospheric crude oil distillation units. Includes all crude oil, lease condensate, natural gas plant liquids, refinery feedstock, liquefied refinery gases, slop oils, and other liquid hydrocarbons produced from tar sands and oil shale.
    Gross product worth
    In oil trade, this is the weighted average value of all refined product components (less an allowance for refinery fuel and loss) of a barrel of the marker crude. Calculated by multiplying the spot price of each product by its percentage share in the yield of the total barrel of crude.
    Ground-source heat pump
    Coupling of a heat exchanger with a heat source from the shallow subsurface in a configuration that can pipe a fluid, such as an antifreeze solution, underground to gather heat and use it to raise the temperature of air or water for space heating or hot water. Can be sized for individual homes, collections of buildings or industrial facilities. Depending on latitude, ground temperatures are relatively stable and range from 7 °C to 21 °C. They are warmer than the air above it during the winter and cooler than the air in the summer. The shallowest systems are typically 1.5-2 metres deep, whereas vertical loop systems can reach more than 100 metres deep. Configuration can be closed loop, open loop or hybridised with other thermal resources. Can be arranged horizontally or vertically underground. Also called geothermal heat pump.

  • H

    Halogen lamp
    A type of incandescent lamp that contains a tungsten filament within a mixture of an inert gas and a small amount of a halogen, such as iodine or bromine. Like other incandescent lamps, halogen lamps are being replaced by light-emitting diodes, which are considerably more efficient, using around 80% less energy.
    Halogen lighting
    See halogen lamp.
    Handy vessel
    Oil tankers with a capacity of 27 000 to 37 999 deadweight tons. Along with other smaller tankers, these can carry clean or dirty cargoes depending on the vessel or trade route. See also Panamax, Handymax, Suezmax, Aframax and very large crude carrier.
    Handymax
    Oil tankers with a capacity of 38 000 to 49 999 deadweight tons. Along with other smaller tankers, these can carry clean or dirty cargoes depending on the vessel or trade route. See also Handy vessel, Aframax, Panamax, Suezmax and very large crude carrier.
    Hard coal
    A solid fossil fuel. Has a gross calorific value over 23 860 kJ/kg (ash-free and moist air at 30 °C and relative air humidity of 96%), and with a mean random vitrinite reflectance of at least 0.6. Hard coal comprises coking coal, other bituminous coal and anthracite (steam coal). See also lignite.
    Hard coal briquettes
    Composition fuels manufactured from hard coal, produced by briquetting under high pressure with or without the addition of a binding agent. In IEA statistics, "energy industry own use" includes consumption by briquetting plants. See also brown coal briquettes.
    Heat crack
    The difference between the price of heating oil and the price of crude oil.
    Heat pump
    An electrical device for space heating, space cooling or for heating water. Transfers thermal energy from an ambient environment using a refrigeration cycle (vapour compression or expansion of a refrigerant working fluid). This can include the extraction of heat from the outside air (air-source heat pump) or shallow subsurface (ground-source heat pump), and also from other nearby heat sources such as exhaust heat as a means of augmenting the output of a primary heating system. May be designed to operate reversibly to provide air conditioning as well as heating, or only to provide cooling (typically labelled simply as an air conditioner). Varies in size from supplying one room to feeding into a district heating system or industrial process. The efficiency of a heat pump is usually such that the heat delivered is several multiples of the energy contained in the input electricity. This efficiency is expressed as the coefficient of performance (COP) or seasonal coefficient of performance (SCOP). In energy statistics, "heat pumps" includes heat produced for sale by heat pumps in transformation only [JF100], and not from heat pumps that are operated within the residential sector, where it is the electricity consumption that would appear as residential use.
    Heating degree day
    A measurement to describe the overall need for heating in buildings. The number of degrees that a day’s average temperature is below a given temperature (normally 18 °C). This temperature is the point below which the consumer is assumed to use energy for space cooling. See also cooling degree day.
    Heating oil
    See light heating oil.
    Heavy crude
    Oil that has an API gravity of less than 20°.
    Heavy fuel oil (residual)
    In energy statistics, oils that make up the distillation residue. Includes all residual fuel oils, including those obtained by blending. Its kinematic viscosity is above 10 cSt at 80 °C. The flash point is always above 50 °C and the density is always more than 0.90 kg/l.
    Heavy gasoil
    A type of gasoil generally blended into fuels such as marine diesel oil. Typically has a lower sulphur content but is also denser and more viscous, with a lower cetane number than other diesel fuel. Distils between 380 °C and 540 °C
    Heavy industries
    Iron and steel, chemicals and cement.
    Heavy oil
    An asphaltic, dense and viscous naturally occurring oil that is chemically characterised by its content of asphaltenes (very large molecules incorporating most of the sulphur and perhaps 90% of the metals in the oil). Has an API gravity of 10° to 22°. Mostly found at the margins of geologic basins and thought to be the residue of formerly light oil that has lost its light molecular weight components through degradation by bacteria, waterwashing and evaporation.
    High-sulphur fuel oil
    Heavy fuel oil with sulphur content higher than 1%.
    High-voltage direct current (HVDC)
    A means of transmission of electricity that takes advantage of the lower energy losses at high voltage and the lower material requirements of direct current lines compared to alternating current. Often used over long distances to connect alternating current transmission systems that are not synchronised. The preferred technology for undersea transmission links. Most HVDC links use voltages between 100 kV and 800 kV, but can reach above 1 000 kV over distances of over 3 000 km.
    Higher heating value (HHV)
    A measure of the energy content of a fuel and the basis of one of two approaches to calculating the efficiency of a process using that fuel (the other being lower heating value). Defined as the amount of heat released by a specified quantity (initially at 25 °C) once it is combusted and the products have returned to a temperature of 25 °C, which takes into account the latent heat of vaporisation of water in the combustion products. As such, it allows a comparison of the total efficiency of sets of processes that seek to extract the maximum heat from water vapour produced by combustion, such as co-generation or other forms of waste heat utilisation. Also known as gross calorific value or gross energy. See also lower heating value.
    Horizontal and directional drilling
    A means of accessing energy resources when vertical drilling is impractical or the deposit is situated in a thin geological layer. Enables deposits to be reached without additional bore holes. While most frequently associated with the recovery of tight oil and gas from shale formations, the technique is also used in other parts of the oil and gas sector, CO2 storage and geothermal energy. As of 2023, the longest well drilled with horizontal and directional methods is 15.2 km long.
    Hot dry rock
    A type of enhanced geothermal system in which the target rock formation is between 150 °C and 650 °C, and 3-10 km underground. Recovery of heat by injection of a working fluid such as water or supercritical CO2 could enable the use of an abundant heat source under the earth's surface.
    Hot water storage
    An approach to energy storage that stores thermal energy as hot water. Typically used to displace heat consumption to a time later than heat generation. The most common form is in tanks in people's homes, which have been used for many decades to temporally balance electricity supply and demand. Large facilities can be found in district heating systems, including in the linepack (the mass of water contained in the pipes at a given moment) of the system. As of 2023, a 56 million litre tank is under construction in Germany for district heating.
    Hybrid electric vehicle (HEV)
    A vehicle with two drivetrains. In IEA analysis, refers to road vehicles with internal combustion engine and electric drivetrains but without an option to recharge the electric battery from an external power source (i.e. not a plug-in hybrid electric vehicle). Sometimes also called conventional hybrid.
    Hydro
    See hydropower.
    Hydrocarbon
    An organic compound consisting entirely of hydrogen and carbon.
    Hydrocracking
    A refining process that uses catalysts and hydrogen at high pressures to convert heavy oils (fuel oil components) to lighter and more valuable products (notably naphtha and middle distillate components). The process can handle high-sulphur feedstock without prior desulphurisation, yielding low-sulphur blending components. Also used in the production of hydrotreated vegetable oil .
    Hydroelectricity
    See hydropower.
    Hydrogen
    The lightest chemical element, which has a variety of industrial and energy applications. As of 2023, most large-scale hydrogen production is for the production of ammonia-based fertilisers or for use in hydrocracking and hydrotreating of oil at refineries. While this hydrogen could be used in a variety of energy applications as a substitute for fossil fuels, which could reduce greenhouse gas emissions, its environmental impact is highly dependent on the manner in which it is produced. Hydrogen that has an environmental impact consistent with the goal of achieving net zero emissions is low-emissions hydrogen. In IEA analysis, total hydrogen demand includes gaseous hydrogen for all uses, including transformation into hydrogen-based fuels and biofuels, power generation, oil refining, and on-site production and consumption. Final consumption of hydrogen includes gaseous hydrogen in end-use sectors, excluding transformation into hydrogen-based fuels and biofuels, power generation, oil refining and on-site production and consumption. Has a specific energy content of 120.1 MJ/kg on a lower heating value basis. 
    In recent years, colours have been vaguely used to refer to different hydrogen production methods. For example, “grey” usually refers to the production of hydrogen from unabated natural gas, “blue” is from fossil fuels with CCUS and “green” is from renewable electricity. As the environmental impacts of each of these production routes can vary considerably by energy source, region and type of CCUS applied, colour terminology is not used by the IEA.
    Hydrogen-based fuels
    Includes ammonia and synthetic hydrocarbons (gases and liquids) that derive their energy content from a pure (or nearly pure) hydrogen feedstock. If produced from low-emissions hydrogen, these fuels are low-emissions hydrogen-based fuels.
    Hydropower
    An energy source that converts the potential and kinetic energy of water into electricity. In energy statistics, the electricity output is taken as a primary energy source. Includes large hydropower, small hydropower and micro hydropower (including run-of-river), but excludes ocean energy. In energy statistics, hydropower does not include pumped-storage hydropower.
    Hydroskimming refinery
    An oil refinery that, unlike a topping refinery, has the ability to produce higher-octane gasoline and lower-sulphur distillate thanks to the addition of naphtha reforming and desulphurisation process units.
    Hydrothermal
    Conventional sources of geothermal energy that allow hot water or steam to be brought to the surface without fracturing or heat exchangers. A source of lithium.
    Hydrotreated esters and fatty acids
    See hydrotreated vegetable oil.
    Hydrotreated vegetable oil
    A liquid biofuel made by the hydrocracking or hydrogenation of vegetable oil, mainly to remove oxygen from the fatty acids in vegetable oils. This contrasts with other biodiesels from vegetable oils that use methanol in a transesterification reaction. Hydrocracking breaks big molecules into smaller ones using hydrogen while hydrogenation adds hydrogen to molecules. Most HVO is designed to be a diesel substitute, but HVO can also replace gasoline, propane, kerosene and other chemical feedstocks. HVO tends to have higher oxidation stability than transesterification biodiesel and is less prone to bacterial growth, making it suitable for stationary, standby applications. The environmental impact of HVO depends on the type of bioenergy input and the method by which the hydrogen is produced. To be a low-emissions fuel, the hydrogen used for HVO needs to be low-emissions hydrogen, which may or may not have biogenic origins.
    Hydrotreating
    A refining process for treating petroleum fractions from atmospheric or vacuum distillation units (e.g. naphtha, middle distillates, reformer feeds, residual fuel oil, and heavy gasoil) and other petroleum streams (e.g. cat-cracked naphtha, coker naphtha, gasoil) in the presence of catalysts and substantial quantities of hydrogen. Hydrotreating results in desulphurisation, removal of substances that deactivate catalysts (e.g. nitrogen compounds) and conversion of olefins to paraffins to reduce gum formation in gasoline.

  • I

    Ice storage
    A type of thermal energy storage that uses energy to freeze water and then uses it as a source of cooling at a later time. A standard application is the production of ice at night using a heat exchanger followed by passing water through pipes in the ice during the day to boost a chiller for air conditioning, for example for a district cooling system or campus air conditioning. Capital investment in chillers is minimised by running them 24 hours per day and off-peak electricity can be used at night. Another form of ice storage is in saturated ground penetrated by boreholes.
    IEA member countries
    See https://www.iea.org/about/membership.
    IEA Monthly Oil Statistics
    Monthly data on oil production for all OECD member countries, and imports, exports, refinery outputs and net deliveries for major product categories for all OECD regions. Includes crude and products trade by source and destination for OECD Member countries, submitted in tonnes. These figures, converted into barrels, are used in the Oil Market Report and the Annual Statistical Supplement.
    IEA refining margins
    A measure of the value contribution of an oil refinery per unit of input. The IEA has a set of global indicator refining margins for primary refined product markets in Northwest Europe, the Mediterranean, the US Gulf Coast and Midcontinent, and Singapore. IEA global Indicator Refining Margins are calculated for various complexity configurations, each optimised for processing the specific crude(s) in a specific refining centre. Margins include energy cost, but exclude other variable costs, depreciation and amortisation. Consequently, reported margins should be taken as an indication, or proxy, of changes in profitability for a given refining centre. No attempt is made to model or otherwise comment upon the relative economics of specific refineries running individual crude slates and producing custom product sales, nor are these calculations intended to infer the marginal values of crude for pricing purposes. The refinery margins are based on indicator refinery yields derived from KBC’s Petro-SIM simulation. These yields are used by both IEA and KBC to generate indicative refining margins for these main products markets, to be referenced as “KBC/IEA Global Indicator Refinery Margins”. The IEA uses Argus Media Ltd price input for all refinery margin calculations.
    For a full description of the methodology, please refer to the IEA Refinery Margins – Methodology Notes document: https://iea.blob.core.windows.net/assets/61137649-cd7e-4823-8990-4eaf4457ff0b/IEARefineryMarginMethodologyJuly2022.pdf
    IEA upstream investment cost index
    An indicator developed by the IEA to monitor year-on-year cost trends in the upstream oil and gas sector. Measures the weighted average annual change of capital costs for exploration and development incurred by operating companies for the entire upstream sector across all regions and assets. A composite indicator that reflects prices for cement, steel and other construction materials and equipment, as well as the cost of sector-specific labour, drilling rigs and oilfield services. Calculated by weighting the average capital spending of two separate exploration and production indices on the basis of disaggregated historical data for the different key components within these two activities. Captures the yearly evolution of costs related to the acquisition of seismic data, project management, well drilling and completion, and the construction of production facilities, as well as the costs of labour, materials and equipment that are incorporated into charges for drilling, completion, related services and facilities. See also USICI.
    IEA upstream shale investment cost index
    An indicator developed by the IEA to monitor year-on-year cost trends in the upstream shale oil and gas sector. Aims to assess trends in underlying costs incurred directly by operating companies. Tracks the inflation rate of capital costs associated with the drilling and completion of modern shale wells, as well as the construction of required facilities for production across the US shale industry. Built as the weighted average of representative components for each of these key activities, including drilling, completion and field facilities. A blended indicator that takes into account time evolution of rig rates, cost of fuel, steel and other raw materials, fracking equipment rates and chemical costs, as well as changes to costs related to a specialised workforce required for the different services. See also UICI.
    Imports
    Imports of energy products comprise all fuel and other energy products entering a national territory. Goods simply being transported through a country (goods in transit) and goods temporarily admitted are excluded, while reimports (i.e. domestic goods exported but subsequently readmitted) are included. The bunkering of fuel outside the reference territory by national merchant ships and civil aircraft engaged in international travel is also excluded from imports.
    Improved cook stoves
    In energy access analysis and statistics, comprises intermediate and advanced improved solid bioenergy cook stoves (ISO tier > 1). Excludes basic improved stoves (ISO tier 0-1).
    In-front-of-the-meter
    In electricity grids, equipment that is external to the electricity consumer. Includes transformers and hardware on the distribution grid, as well as electricity storage and electricity generators that are not "behind-the-meter".
    Inaccessible
    In cases of both undiscovered and discovered CO2 storage, resources can be defined as inaccessible if they are not to be developed for storage at the current time. An example of an inaccessible resource would be one found in a jurisdiction where regulatory regimes prohibit storage.
    Incandescent lamp
    An electric lamp with a wire filament inside a glass bulb containing a vacuum or inert gas. The filament glows when heated by an electric current being passed through it. Incandescent bulbs consume around six times more energy than light-emitting diodes and have much shorter lifetimes. Includes halogen lamps.
    Incandescent lighting
    See incandescent lamp
    Incomplete flaring methane emissions
    Emissions of methane that occur when natural gas that cannot be used or recovered economically is burned instead of being sold or vented. The vast majority of the natural gas is converted into CO2 and water, but some portion may not be combusted and is released as methane into the atmosphere. See also: flaring, fugitive methane emissions, methane emissions, and vented methane emissions.
    Independent oil company (IOC)
    An oil and gas company that is distinguished from the vertically integrated majors in the industry by its relatively small size and its participation in only a limited portion of the value chain, usually upstream. Independent of government ownership, unlike national oil companies.
    Independent power producers
    A power generator that is not a regulated utility (or otherwise involved in transmission and distribution), but which makes electricity available for sale to utilities or the electricity users.
    Independent storage
    In the oil sector, storage owned by independent operators and rented to third parties. Mostly located at global refining and trading hubs in the Amsterdam-Rotterdam-Antwerp (ARA) area, New York Harbor, Singapore and the Caribbean. Independent oil stocks represent a small but important part of total industry stocks as they give a key indicator of what is happening to discretionary stocks. Information on independent storage can be difficult to collect as it is often considered proprietary information by producing countries and data often lie outside the more formal data collection systems.
    Independents
    See independent oil company.
    Indirect land use change
    Changes in the way that land is used resulting from modified economic incentives rather than direct policy action. Often refers to the release of greenhouse gas emissions (CO2 stored in trees and soil) that happens when the use of the land is changed. One example is the conversion of land to conventional bioenergy production due to policy incentives that make liquid biofuels production attractive. The greenhouse gas emissions in such a case offset part of the benefit of switching from fossil fuels to liquid biofuels. See also agriculture, forestry and other land use .
    Induced innovation
    In the analysis of technology innovation, refers to improvements in the performance or reductions in the cost of technologies that arise as innovators respond to "demand pull" factors, including government policies that make markets for certain technologies more lucrative and less risky. A major source of "learning-by-doing" and typically responsible for a large share of innovation overall, including invention and R&D.
    Industrial spirit
    Light hydrocarbon oils distilling between 30 °C and 200 °C. There are seven or eight grades of industrial spirit, depending on the position of the cut in the distillation range. The grades are defined according to the temperature difference between the 5% volume and 90% volume distillation points (which is not more than 60 °C). Mainly for non-energy uses.
    Industry stocks
    Primary stocks owned by oil companies, traders and other organisations except those holding government-controlled stocks. Include stocks held by industry to meet IEA, EU and national emergency reserve commitments.
    Inertial confinement fusion
    A type of nuclear fusion reactor initiated by compressing and heating fuel pellets, which produce shock waves. See also: magnetic confinement fusion.
    Integrated gasification combined cycle (IGCC)
    A type of power plant in which a solid or liquid fuel (coal, heavy oil or solid bioenergy) is gasified, followed by use of the resulting synthesis gas (syngas) for electricity generation in a combined-cycle power plant. Lower emissions can be achieved by adding steps after gasification to shift the composition of the syngas towards CO2 and hydrogen and then capturing the CO2 for CO2 storage so that the fuel used in the combined cycle is low-emissions hydrogen. Configurations can include a source of oxygen to increase CO2 formation in an oxygen-rich gasification environment.
    Integrated solar combined cycle (ISCC)
    A proposed type of power generator composed of a concentrating solar power plant and a combined-cycle gas turbine power plant fired with a gaseous fuel such as natural gas. Depending on gas prices and any penalties for CO2 emissions, the combined plant has the potential to be more dispatchable than a concentrating solar power plant without storage and to produce electricity that is cheaper than standalone concentrating solar power and combined-cycle gas turbine plants.
    Intergovernmental Panel on Climate Change
    An intergovernmental body of the United Nations whose job is to advance scientific knowledge about climate change caused by human activities. Prepares comprehensive assessment reports on the state of scientific, technical and socio-economic knowledge of climate change, its impacts and future risks, and options for reducing the rate at which climate change is taking place. Also produces special reports on topics agreed by its member governments, as well as methodology reports that provide guidelines for the preparation of greenhouse gas inventories. For more information: https://www.ipcc.ch/.
    Intermittency
    See variable renewable energy.
    Intermittent
    See variable renewable energy.
    Internal combustion engine (ICE)
    A heat engine in which the combustion of a fuel occurs with an oxidiser (usually air) in a combustion chamber. The term is usually applied to denote a reciprocating engine as the means of generating motive force in a vehicle or stationary electricity generator, such as a backup diesel genset. Can be based on spark ignition (typically associated with gasoline-type fuels) and compression ignition (typically associated with diesel-type fuels). Hydrogen and hydrogen-based fuels can also be used.

    The designation of an ICE as "two stroke" (typically found in two-wheelers) or "four stroke" (the most common ICE in a car or truck) indicates whether the four integral processes of intake, compression, power and exhaust take place in two or four revolutions of crankshafts ("strokes").

    ICE vehicles are often contrasted with electric vehicles, which do not rely on combustion.
    International oil company
    An integrated oil and gas company listed on the US or European stock markets. The upstream division represents the majority of the financial value, but in physical terms most of these companies are net buyers of oil for their refining operations, where throughputs generally exceed the company’s crude production. The decoupling of the marketing of their upstream production and supply to their refineries makes them active players in the international oil market. They have historically focused on large, capital-intensive projects. The majors are examples of IOCs and the terms are often used interchangeably. As of 2023, majors include BP, Chevron, ExxonMobil, Shell, Total, ConocoPhillips and Eni. See also national oil company.
    International Renewable Energy Agency
    An intergovernmental organisation mandated to facilitate cooperation, advance knowledge, and promote the adoption and sustainable use of renewable energy. For more information: https://www.irena.org/
    Isomerisation
    An oil refining process that alters the fundamental arrangement of atoms in the molecule without adding or removing any atoms from the original material. Isomerisation is used to convert normal butane into isobutane (iC4), an alkylation process feedstock, and normal pentane and hexane into isopentane (iC5) and isohexane (iC6) (high-octane gasoline components). See octane number.

  • J

    Jet fuel
    See aviation fuel
    Joint Organization Data Initiative
    An international collaboration between producer and consumer countries to improve the availability and reliability of data on petroleum and natural gas and to moderate undue price volatility, thereby increasing investor confidence and contributing to greater stability in energy markets worldwide. Partners include APEC, Eurostat, IEA, OLADE, OPEC and UNSD. Initially named the Joint Oil Data Exercise in 2001, renamed JODI in 2005.
    Joule (J)
    A unit of energy equal to the amount of work done when either: a force of one newton displaces a mass through a distance of one metre in the direction of the force applied; or the energy dissipated as heat when an electric current of one ampere passes through a resistance of one ohm for one second. It is the unit of energy in the International System of Units (SI) and is named after the English physicist James Prescott Joule (1818–1889). 3 600 J = 1 Wh.

  • K

    Kerosene
    A liquid oil product mostly used as an aviation fuel, historically also used as fuel for oil lamps. Comprises refined petroleum distillate intermediate in volatility between gasoline and gas/diesel oil. A medium oil distilling between 150 °C and 300 °C. Has a lower heating value of around 43 MJ/kg. As of 2023, the overwhelming majority of kerosene is derived from crude oil distillation, but synthetic kerosene manufactured from hydrogen and CO2 is beginning to enter the market. If synthetic kerosene is produced from low-emissions hydrogen and a sustainable source of CO2, it is a low-emissions hydrogen-based liquid fuel.
    Kerosene-type jet fuel
    A blend of kerosenes suited to flight conditions with particular specifications, such as freezing point.
    Kilogramme of carbon dioxide equivalent (kg CO2-eq)
    See carbon dioxide equivalent
    Kilowatt hour
    One thousand watt hours. See watt hour
    Knowledge management
    A category of innovation policies that addresses the need for knowledge protection incentives, such as intellectual property systems for inventors, and also enables knowledge exchange among stakeholders. Can include networks for knowledge exchange, open access publishing requirements or international co-operation agreements to ensure that new knowledge is documented and flows to other users and into new products. See also: resource push, socio-economic support and market pull.

  • L

    Land use change
    Changes in the way that land is used. The term often refers to the release of greenhouse gas emissions (CO2 stored in trees and soil) that happens when the use of the land is changed, which is a component of agriculture, forestry and other land use. Includes indirect land use change . See also land use, land use change and forestry .
    Land use, land use change and forestry
    A term used in greenhouse gas emissions accounting and analysis that groups together the emissions impacts from land use, land use change and forestry. Since 2006 largely superseded by the term agriculture, forestry and other land use, which incorporates all agricultural emissions (excluding those from fossil fuel combustion in agricultural machinery). See also agriculture, forestry and other land use and land use change.
    Landfill gas
    A gaseous fuel captured from the gases produced during anaerobic digestion of organic matter in landfill sites. Typically has a methane content of 45% to 60%. A type of biogas and a renewable energy source.
    Large hydro
    See large hydropower.
    Large hydropower
    A type of hydropower generation facility that usually involves the creation of a reservoir replenished by a natural watercourse. In IEA analysis, large hydropower sites are those above 10 MW. The vast majority of installed hydropower in the world is large hydropower.
    Lead time
    In IEA work this generally refers to the elapsed time between a final investment decision and the end of commissioning of an asset, such as a power plant or oil field. Represents the period over which CAPEX is spent, and used in IEA modelling to convert between overnight costs and annualised spending.
    Leaded motor gasoline
    Motor gasoline with tetraethyl lead and/or tetramethyl lead added to enhance the octane number. Leaded gasoline damages catalytic converters and was banned in the United States for cars made since 1975. In 2021 Algeria became the last country to ban leaded gasoline in road vehicles. Leaded gasoline has also been a source of lead pollution. As of 2023, it is still used in some off-road vehicles.
    Learning curve
    See learning rate.
    Learning rate
    A term used in relation to innovation and cost declines. Usually expressed as the percentage reduction in cost after each doubling of cumulative installed capacity or output of a defined type of technical equipment. Costs can be expressed either as capital costs (including or excluding installation costs) or, for energy technologies, levelised costs (which account for efficiency improvements). The learning rate is an observation of the combined impacts of improvements to the underlying technology (sometimes called learning-by-researching), improvements to manufacturing techniques and accumulated experience of operators and installers (sometimes called learning-by-doing), economies of scale and changes to input prices. Therefore, a learning rate not only reflects innovation and technological improvements. Learning rates do not follow any fundamental rules and vary widely between technologies and regions. The expression forgetting-by-not-doing has been applied to negative learning rates experienced for technologies with a lack of consistent deployment over time, including nuclear fission in some countries.
    Learning-by-doing
    The accumulation of knowledge from direct experience of undertaking the activity through repetition, trial and feedback. See learning rate.
    Learning-by-researching
    The accumulation of knowledge by devoting R&D resources to the search for new ideas and their development into viable products and services, including prototypes and demonstration projects. See learning rate.
    Levelised cost of electricity (LCOE)
    An indicator of the expected average production cost for each unit of electricity generated by a technology over its economic lifetime. The LCOE combines into a single metric all the cost elements directly associated with a given power technology, including construction, financing, fuel, maintenance and costs associated with a carbon price. It does not include network integration or other indirect costs. For a more complete indicator, see value-adjusted levelised cost of electricity (VALCOE).
    Lge per 100 km
    Litre of gasoline equivalent per 100 km. A standardised measure of vehicle fuel economy (energy efficiency) that represents the expected amount of energy needed to propel a road vehicle and its typical contents over a distance of 100 km. The IEA reports values consistent with the Worldwide Harmonised Light Vehicles Test Procedure testing methodology.
    Licence round
    In the oil sector, a process by which a government offers a stated number of specified areas to oil companies for exploration. Concludes with the award of licences to successful bidders. Has also been used for other resources, including critical minerals and CO2 storage.
    Licensing round
    See licence round.
    Life cycle assessment
    A methodology for assessing the environmental impacts associated with all the stages of the life cycle of a commercial product, process or service. LCA studies involve inventories of the energy and materials that are required across the value chain of the product, process or service, and estimation of the corresponding emissions to the environment. Procedures for conducting LCAs are included in the 14000 series of environmental management standards of the International Organization for Standardization (ISO). LCA approaches are increasingly being integrated into regulations, for example standards for the certification of low-emissions hydrogen.
    Light crude
    See API gravity.
    Light fuel oil
    Light distillate fuel oils that can be used for heating purposes (heating oil). In the IEA World Energy Prices database, light fuel oil prices are included within kerosene.
    Light heating oil
    A grade of gasoil for industrial and commercial uses. A medium distillate hydrocarbon, distilling between 180 °C and 380 °C.
    Light petroleum products
    Low-density products that flow freely at room temperature, have low viscosity, low specific gravity and high API gravity. Includes liquefied petroleum gas, naphtha and gasoline.
    Light-emitting diode (LED)
    An efficient solid-state device for converting electrical energy to light. Can be used in all type of lights, including electronic devices and screens. Up to six times more efficient than conventional technologies such as incandescent and halogen lamps, and can provide equivalent or better lighting. Last much longer than incandescent lamps, meaning fewer replacements are required. As of 2022, over 50% of the global lighting market used LED technology. See also: incandescent lighting, halogen lighting and fluorescent lighting.
    Light-water reactor
    A type of nuclear fission reactor that uses normal water (not heavy water) as both a moderator and coolant. Includes pressurised water reactor, boiling water reactor and supercritical water reactor.
    Lightering
    Transferring cargo from one vessel to another (typically, a smaller one). Generally done to facilitate the onward transit of the cargo, where access to larger vessels is restricted (e.g. due to draft restrictions). Examples of lightering in the oil sector include very large crude carriers on to Aframaxes in the US Gulf to allow cargoes to be taken to refineries via smaller waterways and Aframaxes onto barges in Northern Europe to deliver to inland terminals.
    Liquefaction
    The process of converting a gaseous fuel to the liquefied state by cooling and applying pressure. Usually refers to the liquefaction step of the liquefied natural gas value chain, but could also apply to other gaseous fuels, including hydrogen. Natural gas liquefies at -162 °C and the maximum transport pressure is set at around 25 kPa. The liquefied natural gas liquefaction process also involves removal of impurities such as dust, acid gases, helium, water and heavy hydrocarbons. Liquefied natural gas takes up about 1/600th the volume of natural gas in the gaseous state, i.e. 1 bcm of LNG contains the energy in 600 bcm of standard natural gas. See also regasification.
    Liquefaction terminal
    A facility, usually at a sea port, for liquefaction of shipped liquefied gaseous fuels such as liquefied natural gas or, potentially, hydrogen.
    Liquefaction/regasification plants
    A category in energy statistics that refers to the energy used by liquefaction and regasification plants for liquefied natural gas.
    Liquefied natural gas (LNG)
    A form of natural gas that is suited to being transported by sea. Natural gas is liquefied by reducing its temperature to -162 °C at atmospheric pressure, reducing its space requirements for storage and transport by a factor of over 600. As a means of trading natural gas, use of LNG has increased dramatically in recent decades, from around 30 bcm in 1980 to 150 bcm in 2000 to around 500 bcm in 2022. As of the early 2020s, this represents around half of the global gas trade.
    Liquefied petroleum gas (LPG)
    Liquefied propane (C3H8) and butane (C4H10) or mixtures of both. Commercial grades are usually mixtures of the gases with small amounts of propylene, butylene, isobutene and isobutylene stored under pressure in containers.
    Liquid biofuels
    Liquid fuels derived from biomass or waste feedstock, including ethanol, biodiesel and biojet fuels. They can be classified as conventional and advanced biofuels according to the combination of feedstock and technologies used to produce them and their respective market maturity. Unless otherwise stated, biofuels are expressed in energy-equivalent volumes of gasoline, diesel and kerosene.
    Liquid fuels
    Liquid material that is used to produce heat and power. Includes crude oil, oil products, liquid biofuels, synthetic oil products and low-emissions hydrogen-based fuels such as liquid synthetic hydrocarbons.
    Liquids unloading
    The removal of accumulated fluids from natural gas well bores either by venting (“blowing down”) or using artificial lift techniques (e.g. plunger lifts). Liquids unloading can be a significant source of methane emissions.
    Litre of gasoline equivalent (Lge)
    A unit of energy content equal to the chemical energy in one litre of a standardised gasoline liquid fuel. 1 lge = 32 MJ. 1 litre of diesel contains 1.077 lge. 1 litre of ethanol contains 0.631 lge. 1 litre of FAME biodiesel contains 0.976 lge.
    Load factor
    See capacity factor.
    Long position
    The net exposure of a trader (or group of traders) when their bought (long) physical or paper exposure exceeds their sold (short) positions. See also short position.
    Long ton
    A unit of mass that is not part of the International System of Units. Still used to specify the size of some oil tankers, for example as deadweight tonnage. Equal to 1.016 tonnes. See also short ton.
    Low carbon fuel standard
    A policy measure designed to reduce the average emissions intensity of fuel supplied in the relevant market by incentivising regulated entities to fund the most cost-effective mix of technological or other changes. Usually places an obligation on retail fuel suppliers to demonstrate that the products they sell meet an annual average carbon intensity target, which declines over time. Compliance is achieved by holding carbon intensity certificates that are generated when each unit of fuel enters the supply chain. These certificates are accrued by fuel suppliers when they procure products for sale and the certificates can also be traded between fuel suppliers if their average carbon intensity position is too high or low. The Californian LCFS is an example.
    Low-emissions fuels
    Includes bioenergy, low-emissions hydrogen and low-emissions hydrogen-based fuels.
    Low-emissions gases
    Includes biogas, biomethane, low-emissions hydrogen and low-emissions synthetic methane.
    Low-emissions hydrogen
    Includes hydrogen which is produced through water electrolysis with electricity generated from a low-emissions source (such as renewables, e.g. solar and wind turbines, and nuclear). Hydrogen produced from biomass or from fossil fuels with carbon capture, utilisation and storage (CCUS) technology is also counted as low-emissions hydrogen. Production from fossil fuels with CCUS is included only if upstream emissions are sufficiently low, if capture – at high rates – is applied to all CO2 streams associated with the production route, and if all CO2 is permanently stored to prevent its release into the atmosphere. The same principle applies to low-emissions feedstocks and hydrogen-based fuels made using low-emissions hydrogen and a sustainable carbon source (of biogenic origin or directly captured from the atmosphere).
    Low-emissions hydrogen-based fuels
    Fuels produced from low-emissions hydrogen. Includes ammonia, methanol and other synthetic hydrocarbons (gases and liquids) made from low-emissions hydrogen when any carbon inputs, e.g. from CO2, are not from fossil fuels or fossil-derived process emissions.
    Low-emissions hydrogen-based liquid fuels
    A subset of low-emissions hydrogen-based fuels that includes only ammonia, methanol and synthetic liquid hydrocarbons, such as synthetic kerosene.
    Low-sulphur diesel
    Diesel with a sulphur content higher than 50 ppm. See also ultra-low sulphur diesel.
    Low-sulphur fuel oil
    Heavy fuel oil with sulphur content lower or equal to than 1%.
    Low-sulphur waxy residue
    Cracked low-sulphur fuel oil with 0.2-0.3% sulphur content. It is mostly supplied by Indonesia.
    Lower heating value (LHV)
    A measure of the energy content of a fuel and the basis of one of two approaches to calculating the efficiency of a process using that fuel (the other being higher heating value). Defined as the amount of heat released by a specified quantity (initially at 25 °C) once it is completely combusted and with the water produced remaining as a vapour. Does not take into account the latent heat of vaporisation of water in the combustion products. As such, it reflects many of today's energy-using processes that do not recover the heat in the water vapour, but it does not allow a comparison of the total efficiency of sets of processes that seek to extract the maximum heat from water vapour produced by combustion, such as co-generation or other forms of waste heat utilisation. Also known as net calorific value or net energy. See also higher heating value.
    Lubricants
    In energy statistics and analysis, oils produced from crude oil for which the principal use is to reduce friction between sliding surfaces and during metal cutting operations.

  • M

    Magnox
    A type of nuclear fission reactor with a graphite moderator and carbon dioxide coolant. Named after the magnesium non-oxidising alloy used to clad the fuel rods. Developed in the United Kingdom in the 1950s with the potential to produce plutonium as well as energy services, the first Magnox power station, Calder Hall, is generally regarded as the world's first nuclear power station to generate electrical power on an industrial scale in 1956. In total 14 Magnox power stations were built, almost all in the United Kingdom, and the last one closed in 2015.
    Major
    A large integrated oil and gas company that is listed on the US or European stock markets. See international oil company.
    Marine energy
    See ocean energy.
    Market pull
    A type of government policy that specifically targets induced innovation via market forces in a given technology area. Effective market pull innovation policies make R&D risks worthwhile for innovators and stimulate investment in innovation, including R&D, to try to capture more of the value placed on the energy service by the market (now or in the future). Market creation by government “pulls” ideas along the innovation process by: raising expectations of future revenue and thus raising innovators’ interest in developing new products; increasing revenue from existing product sales, thereby rewarding investors and enabling reinvestment in R&D, helping to bridge the “valley of death”; and by learning-by-doing via commercial scale-up, which spurs new ideas for improvements and products. Sometimes also referred to as "demand pull", a term that is often contrasted with "technology push" policies for technology deployment without an explicit innovation focus. See also knowledge management, resource push.
    Mean random vitrinite reflectance
    The average of the percentage of light reflected by a statistically meaningful sample of polished vitrinite particles of coal.  
    Megawatt hour (MWh)
    One million watt hours. See watt hour.
    Methane
    A hydrocarbon gas that is the major constituent of natural gas and biogas. Biogas from which impurities have been removed to increase the methane content is known as biomethane. Methane is a potent greenhouse gas with a GWP100 of 27-30 (depending on the measurement system and origin) and a GWP20 of 81-83. Avoiding the leakage and flaring of methane from the production and transport of oil and gas, the mining of coal, the production of biogas and the land-use sector will be a vital measure in the achievement of net zero greenhouse gas emissions. Methane has a specific energy of 55.5 MJ/kg (higher heating value basis).
    Methane emissions
    Methane emission from fossil fuel operations were estimated at 120 Mt. As of 2023, the concentration of methane in the atmosphere is more than 2.5 times greater than its pre-industrial levels and methane is responsible for around 30% of the rise in global temperatures since the Industrial Revolution. Rapid and sustained reductions in methane emissions are key to limiting near-term global warming and improving air quality. Includes fugitive methane emissions, vented methane emissions and incomplete flaring methane emissions. See also methane.
    Methane pyrolysis
    A term for a set of processes that decompose methane (usually from natural gas) into hydrogen and carbon without any CO2 emissions from the chemical process. Innovation is focused on reducing the temperatures required to overcome the strong C-H bond, leading to different technological routes: thermal, catalytic and plasma pyrolysis. In thermal decomposition, the reaction occurs without the presence of a catalyst and temperatures above 1 200 °C are typically needed to obtain a reasonable yield. In catalytic decomposition this can be reduced to below 1 000 °C. Achieving such high temperatures without fossil fuel combustion is a challenge, and plasma pyrolysis (powered by electricity) is thought to be a promising option. Moreover, it is the most advanced pyrolysis route as of 2023, with a pre-commercial demonstration plant operating in the United States since 2021 and a plant 14 times larger planned. As of 2023, there are divergent views on the economics of methane pyrolysis and whether the carbon by-product can find a commercial market at scale or will need to be safely disposed of. Hydrogen produced via methane pyrolysis has the potential to be equivalent to low-emissions hydrogen, but the overall emissions intensity depends on the fate of any by-products and other stages of the value chain such as conditioning and transport.
    Methane venting
    The intentional release of methane into the environment from oil and gas operations, often for safety reasons, due to the design of the facility or equipment (e.g. pneumatic controllers) or operational requirements (e.g. venting a pipeline for inspection and maintenance). See also: methane emissions, fugitive methane emissions, and incomplete flaring methane emissions.
    Methanol
    A chemical compound composed of carbon, hydrogen and oxygen. One of the world's most widely used industrial chemicals. Can also be used as a fuel, including in fuel cells. Because it has the potential to be produced from low-emissions hydrogen and sustainable sources of carbon (whether in the form of CO2 or synthesis gas made from biomass), low-emissions methanol is a candidate to power ships and other energy-intensive equipment in a net zero energy future. In energy statistics, methanol refers to energy used in the manufacture of methanol and intermediate products in the production of methanol. Methanol has a specific energy of 22.9 MJ/kg (higher heating value basis).
    Methanol-to-olefin
    A process for converting methanol to olefins, which are bulk chemical precursors. Most commonly used when coal is the primary feedstock for bulk chemical production, not petroleum products. Typically preceded by the production of methanol from synthesis gas made via coal gasification.
    Methyl tertiary butyl ether
    An additive used for gasoline blending, particularly for high-octane grades. Legislative changes have led to its increasing substitution by ethanol.
    Micro hydropower
    Small-scale hydropower plants with a capacity of 100 kW or less.
    Microgrid
    A group of interconnected loads (energy-consuming devices) and energy sources that acts as a single controllable and self-sufficient entity. Typically does not exceed a few megawatts of total capacity. Can be for electricity or gas distribution, although electricity is the most common. Most serve a discrete local area, such as a campus, hospital complex, industrial zone or neighbourhood. Increasingly deployed to provide off-grid access to electricity in emerging market and developing economies by combining solar PV and battery storage. If grid connected, capable of disconnecting to operate in "island mode". Local grids for the supply of heat or cooling are generally referred to as district heating and district cooling systems. See also energy access.
    Middle distillates
    Products refined from crude oil that have between 10 and 20 carbon atoms, a density of not more than 0.860 kg/l at 15 °C, and a flashpoint above 60 °C. Includes jet fuel, diesel and heating oil.
    Midstream
    In energy supply, the stage of the supply chain that transports unprocessed energy resources. In the oil and gas industry, it includes shipping and transporting crude oil or other unrefined energy products. Midstream connects to upstream (exploration and extraction) and downstream (refining, shipping and marketing). See also downstream and upstream.
    Miles per gallon (mpg)
    See lge per 100 km.
    Million barrels per day (mb/d)
    See barrels per day.
    Million British thermal units (MBtu)
    See British thermal unit.
    Million tonnes carbon dioxide (Mt CO2)
    See tonne of carbon dioxide.
    Million tonnes of coal equivalent (Mtce)
    See tonne of coal equivalent.
    Million tonnes of oil equivalent (Mtoe)
    See tonne of oil equivalent.
    Mini-grids
    Small electric grid systems, not connected to main electricity networks, linking a number of households and/or other consumers.
    Minimum operating levels
    The amount of oil stocks required to keep the global supply system operating efficiently. Includes tank bottoms, pipeline fill, etc.
    Mission Innovation
    An intergovernmental initiative to accelerate clean energy innovation, launched in 2015. The IEA works with MI in a number of ways, including, as of 2022, as a participant in the secretariat and data coordinator. See https://www.iea.org/areas-of-work/international-collaborations/mission-innovation.
    Mixed-feed crackers
    Crackers designed to alter their feedstock mix depending on market conditions. See also cracking.
    Modern bioenergy
    Bioenergy excluding the traditional use of bioenergy and other low-efficiency or unsustainable practices. Includes modern solid bioenergy, liquid biofuels and biogases.
    Modern biomass
    See modern bioenergy.
    Modern energy access
    There is no single internationally accepted definition of modern energy access. Includes: household access to a minimum level of electricity; household access to less harmful and more sustainable cooking and heating fuels, and stoves; access that enables productive economic activity; and access for public services.
    Modern gaseous bioenergy
    See biogas.
    Modern renewables
    Renewables excluding the traditional use of bioenergy and other low-efficiency or unsustainable practices. Includes biogases, hydropower, geothermal energy, liquid biofuels, modern solid bioenergy, ocean energy, solar energy, wind.
    Modern solid bioenergy
    Solid bioenergy excluding the traditional use of solid bioenergy and other low-efficiency or unsustainable practices.
    Molten carbonate fuel cell (MCFC)
    A type of fuel cell that has an electrolyte composed of a molten carbonate salt and operates at temperatures of 600 °C and above. Usually designed for use with gaseous carbon-containing fuels such as natural gas and can reach efficiencies above 60% if waste heat is captured and used. Requires CO2 to be delivered to the cathode along with the oxidiser, so can be used to electrochemically separate CO2 from the flue gases of a separate combustion process if they are fed into the MCFC along with the MCFC fuel gas. As of 2023, this approach to CO2 capture has not been demonstrated at commercial scale.
    Molten salt
    See molten salt storage
    Molten salt storage
    A type of thermal energy storage that works by heating an anhydrous liquid salt melt, typically a mixture of nitrate/nitrite salts, which can enable working temperatures of 170-560 °C. During heating or cooling, the liquid salt is passed through a heat exchanger to accept heat from an external source or raise steam for a use such as power generation. Molten salt storage is used in conjunction with concentrating solar thermal power to extend the output of the power plant beyond daylight hours.
    Motor gasoline
    A mixture of some aromatics (e.g. benzene and toluene) and aliphatic hydrocarbons in the C5 to C12 range, blended to form a fuel mixture suitable for use in spark-ignition engines. The distillation range is 25 °C to 220 °C.
    Municipal solid waste (non-renewable)
    A term used in energy statistics. Includes waste produced by households, industry, hospitals and the tertiary sector that contains non-biodegradable materials that are incinerated at specific installations. The quantity of fuel used is reported on a net calorific value basis. See also: non-biogenic waste; municipal solid waste (renewable).
    Municipal solid waste (renewable)
    A term used in energy statistics. Includes waste produced by households, industry, hospitals and the tertiary sector that contains biodegradable materials that are incinerated at specific installations. The quantity of fuel used is reported on a net calorific value basis. See also: non-biogenic waste; municipal solid waste (non-renewable).

  • N

    Naphtha
    Light or medium oils distilling between 30 °C and 210 °C that do not meet the specification for motor gasoline.
    Naphtha-type jet fuel
    A fuel in the heavy naphtha boiling range. ASTM Specification D1655 specifies for this fuel maximum distillation temperatures of 140 °C at the 20% recovery point and 240 °C at the 90% recovery point, meeting Military Specification MIL-T-5624L (Grade JP-4). JP-4 is used for turbojet and turboprop aircraft engines, primarily by the military. Excludes ram-jet and petroleum rocket fuels.
    National oil company (NOC)
    A company in the oil and gas sector that is fully or majority owned by national government, usually involved in upstream and midstream activities and focused on domestic production. An NOC that has both domestic and significant international upstream operations is known as an international oil company.
    Nationally determined contribution (NDC)
    The Paris Agreement requests each country to outline and communicate their post-2020 climate actions, known as nationally determined contributions. They embody efforts by the country to reduce their greenhouse gas emissions and adapt to the impacts of climate change.
    Natural decline rate
    The base production decline rate of an oil or gas field without intervention to enhance production. Expressed as a percentage decrease of the production rate in one year. As of 2023, production from existing conventional fields declines at a rate of roughly 8% per year in the absence of any investment.
    Natural gas
    A gaseous fossil fuel, consisting mostly of methane. Occurs in deposits, whether liquefied or gaseous. In IEA analysis and statistics it includes both non-associated gas originating from fields producing hydrocarbons only in gaseous form, and associated gas produced in association with crude oil production, as well as methane recovered from coal mines (colliery gas). Natural gas liquids, manufactured gas (produced from municipal or industrial waste, or sewage) and quantities vented or flared are not included. Natural gas has a specific energy of 44.09 MJ/kg on a higher heating value basis. Natural gas data in cubic metres (e.g. bcm of natural gas) are expressed on a gross calorific value basis and are measured at 15 °C and at 760 mm Hg (Standard Conditions). Natural gas data expressed in tonnes of oil equivalent, mainly to allow comparison with other fuels, are on a net calorific basis. The difference between the net and the gross calorific value is the latent heat of vaporisation of the water vapour produced during combustion of the fuel (for gas the net calorific value is 10% lower than the gross calorific value).
    Natural gas combined cycle (NGCC)
    See combined-cycle gas turbine.
    Natural gas fuel cell (NGFC)
    A fuel cell designed to transform the chemical energy in natural gas into electricity, such as a molten carbonate fuel cell or solid oxide fuel cell.
    Natural gas liquids
    Liquid or liquefied hydrocarbons produced in the manufacture, purification and stabilisation of natural gas. NGLs are portions of natural gas recovered as liquids in separators, field facilities or gas processing plants. NGLs include, but are not limited to, ethane (when it is removed from the natural gas stream), propane, butane, pentane, natural gasoline and condensates.
    Natural gas vehicle
    A road vehicle designed to run on natural gas, for example compressed natural gas. Includes internal combustion engine and fuel cell electric vehicles.
    Natural gasoline
    A commodity product commonly traded on natural gas liquid markets that comprises liquid hydrocarbons (mostly pentanes and hexanes) and generally remains liquid at ambient temperatures and atmospheric pressure. Natural gasoline is equivalent to pentanes plus.
    Net calorific value
    See lower heating value.
    Net energy
    See lower heating value.
    Net product worth
    In the oil sector, this is gross product worth minus variable refinery operating costs (feed-dependent costs for power, water, chemicals, additives, catalyst and refinery fuels beyond own production), fixed refinery operating costs (labour, maintenance, taxes and overhead costs adjusted monthly to take account of escalations based on industry cost indices), refinery delivered crude cost (transport and credit allowance costs), transport costs (marginal crude freight, insurance and ocean loss in case of free on board crude, applicable fees and duties, assuming a single voyage for an appropriately sized tanker chartered on the spot market), and credit allowance (representing the financial effect of the time delay between paying for crude versus when it is received in the refinery, e.g. crude credit and crude transit time.
    Net Zero Emissions Scenario (NZE)
    A scenario which sets out a pathway for the global energy sector to achieve net zero CO2 emissions by 2050. It does not rely on emissions reductions from outside the energy sector to achieve its goals. Universal access to electricity and clean cooking are achieved by 2030. The scenario was fully updated in 2023.
    Netback
    In oil trade, this is the sales price at destination minus the full cost of transport (including working capital, the risk of price changes in transit, etc.) from the point of origin.
    Network gases
    Gaseous fuels transported in a pipeline gas network, either separately or blended together. Include natural gas, biomethane, synthetic methane and hydrogen blended in a gas network.
    Nitrogen oxide (NOx)
    A generic term for oxides of nitrogen that contribute to air pollution. Includes NO and NO2. Does not include N2O.
    Nitrous dioxide
    A powerful greenhouse gas. The main components of anthropogenic NO2 emissions are (in order of magnitude) fertilised agricultural soils and livestock manure, runoff and leaching of fertilisers, solid bioenergy burning, fossil fuel combustion and industrial processes, biological degradation of other nitrogen-containing atmospheric emissions and human sewage. NO2 has a GWP100 and GWP20 of 273.
    Non-biogenic waste
    The fraction of waste not classified as bioenergy, i.e. not derived from food, agriculture or other organic matter. Contains a significant share of material derived from fossil fuels. In the absence of more accurate data, the non-biogenic waste fraction is sometimes assumed to be 50% of municipal solid waste by energy content and the rest considered renewable. See also municipal solid waste (non-renewable) and biogenic waste.
    Non-commercials
    In oil trade, these are entities trading commodities in the futures market in the hope of profiting from a change in oil’s value, but not involved in its production, processing or merchandising.
    Non-energy use
    The use of energy products as raw materials for the manufacture of non-energy products, e.g. natural gas used to produce fertiliser, as well as for direct uses that do not involve using the products as a source of energy, nor as a transformation input e.g. lubrication, sealing, roading surfacing, preservation, use as a solvent.
    Non-renewable waste
    See non-biogenic waste.
    Non-reporting
    In oil trade, these are entities whose volume of futures positions in a type of contract remains below the minimum reporting level set by the exchanges and/or the US Commodity Futures Trading Commission.
    Nordics
    Denmark, Finland, Norway and Sweden.
    Normal cubic metre
    A standardised unit of volume applied in the definitions of bcm of natural gas and Nm3 of hydrogen.
    Not-in-my-backyard
    An expression used to signify opposition to a project, such as an energy installation, from people or a community living locally. Often used to contrast this sentiment with the same people's support for similar projects elsewhere. See also BANANA.
    Novel advanced biofuels
    Advanced bioenergy products produced using technologies that are not yet fully commercialised. Includes liquid biofuels from waste and residue feedstocks.
    Nuclear
    Energy released by nuclear fission or nuclear fusion. In IEA analysis and energy statistics, total energy supply from nuclear refers to the heat input and not the electricity output. This heat input is estimated based on the electricity output and a conversion efficiency of 33% unless country- or case-specific information is available.
    Nuclear fission
    A means of harnessing the atomic energy in nuclear fuel, whereby the nucleus of an atom, having captured a neutron, splits into two or more nuclei. In so doing, it releases a significant amount of energy as well as more neutrons. These neutrons then go on to split more nuclei and a chain reaction takes place, creating sufficient heat to elevate the temperature of a working fluid and power an electric generator. As of 2023, all nuclear power plants are based on nuclear fission. See also nuclear fusion.
    Nuclear fusion
    A means of harnessing the atomic energy in nuclear fuel, whereby two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles (neutrons or protons). The difference in mass between the reactants and products is manifested as either the release or absorption of energy, creating sufficient heat to elevate the temperature of a working fluid and power an electric generator, potentially in a self-sustaining series of reactions. Nuclear fusion is the process that powers active or main-sequence stars and other high-magnitude stars. As of 2023, no electricity-producing nuclear fusion plants are yet in operation. See also nuclear fission.

  • O

    Observed decline rate
    The actual change in the production rate of an oil or gas field in one year, or the estimate of how this rate will change in future. Expressed as a percentage decrease of the production rate in one year. The actual change in production rate of a field is not equal to the natural decline rate when there is intervention to stimulate production, including enhanced oil recovery. When expressed for a region comprising multiple fields, the observed decline rate is the aggregation of all the production increases and declines of new and mature oil or gas fields. For natural post-peak decline rates in the range of 5% to 18%, observed decline rates may be in the range of 4% to 12%.
    Ocean energy
    Mechanical energy harvested from ocean currents, tidal movement or wave motion and exploited for electricity generation. Includes: tidal power, wave energy, ocean current power and ocean thermal power. Sometimes called marine energy.
    Octane number
    An indicator of the composition of a gasoline fuel that can be used to predict its performance in specific engine designs. The general rule is that a higher octane number indicates higher performance, but this is not universally applicable. Technically the octane number is a standard measure of a fuel's ability to withstand compression in an internal combustion engine without detonating. It was originally developed to indicate fuel mixtures that are less likely to self-ignite before being reached by the main flame in the combustion chamber, causing high pressure and "knocking" in older engines without modern engine management systems. Highway gasoline engines typically require an octane number of 90 while regulations in most parts of the world have set a threshold above this, for example 95 in the European Union. The octane number is equal to the percentage by volume of 2,2,4-trimethylpentane (iso-octane) in normal heptane that would have the same anti-knocking capability as the fuel under test. The most common type of octane rating worldwide is the Research Octane Number (RON), determined by running the fuel in a test engine with a variable compression ratio under controlled conditions. The octane number performs a similar function for the gasoline market as the cetane number does for diesel.
    Octane rate
    See octane number.
    Off-grid
    A producer or consumer of electricity that is not connected to the main regulated electricity distribution system, or a producer or consumer of gaseous fuels that is not connected to the main regulated gas distribution system. See also mini-grid and microgrid.
    Offshore
    Usually used to refer to energy supply activities that take place in open water, usually at sea. In upstream oil and gas, it includes extraction of natural gas and oil from below the seabed and processing on the seabed or on an offshore platform. Also includes offshore wind, ocean energy, offshore CO2 storage and so-called artificial energy islands.
    Offshore wind
    A type of wind energy, usually electricity, produced by wind turbines installed in open water, typically in the ocean. Includes fixed offshore wind (fixed to the seabed) and floating offshore wind.
    Offshore-loaded
    Oil produced offshore is either moved onshore by pipeline or loaded offshore direct from a floating production, storage and off-loading vessel or a buoy-mooring facility.
    Oil
    A liquid fuel. Usually refers to fossil fuel mineral oil. Includes oil from both conventional and unconventional oil production. In energy statistics, includes petroleum products such as refinery gas, ethane, liquid petroleum gas, motor gasoline, aviation fuel, kerosene, gas/diesel oil, heavy fuel oil, naphtha, white spirit, lubricants, bitumen, paraffin, waxes and petroleum coke. In the IEA Oil Market Report, oil demand additionally includes demand for all liquid fuels, including liquid biofuels.
    Oil and gas fields
    Includes oil fields and gas fields
    Oil and gas well
    Includes oil wells and gas wells
    Oil burden
    A proxy of how much any given economy spends on its oil needs in a given year, used as a leading indicator of potential economic trouble ahead. Typically, the global oil burden hovers around 2% of GDP – except during oil price shocks. Defined as nominal oil expenditure (demand multiplied by the crude price) divided by nominal GDP.
    Oil field
    An area of accumulation of liquid crude oil underground in multiple (potentially linked) reservoirs, trapped by impermeable rock formations. In the energy industry, it is applied to areas worthy of commercial attention. Oil fields may also contain natural gas and be referred to as "oil and gas fields".
    Oil in transit
    A useful proxy measure of oil tanker demand, calculated as the sum of all oil being transported by sea at a given time. Sometimes called oil on water.
    Oil on water
    See oil in transit.
    Oil product
    Traded products derived from, but not including, crude oil. Includes refinery gas, ethane, liquefied petroleum gas, aviation gasoline, motor gasoline, jet fuel, kerosene, gas/diesel oil, fuel oil, naphtha, white spirit, lubricants, bitumen, paraffin waxes, petroleum coke and other oil products.
    Oil refining
    The processes involved in making oil products from crude oil, unfinished oils, natural gas liquids, other hydrocarbons, oxygenates, additives and hydrogen. Includes distillation, cracking, hydrotreating, hydrogenation, treating and blending.
    Oil sands
    A mixture of sands, with some rocks and clay, about 10% bitumen and small quantities of water. There are large deposits in Canada (Athabasca) and Venezuela.
    Oil shale
    A sedimentary rock that yields petroleum products, along with a variety of solid by-products, when heated to above 300 °C in the absence of oxygen. The liquid oil extracted from oil shale, once it is upgraded, is a synthetic crude oil commonly referred to as shale oil. See also tight oil.
    Oil shale and oil sands
    In energy statistics this refers to the sum of oil shale and oil sands. Oil shale and oil sands used as inputs to other transformation processes are also included here (this includes the portion consumed in the transformation process). Shale oil and other products derived from liquefaction are included in other sources under crude oil (other hydrocarbons).
    Oil well
    A drilled hole in the earth's surface for the primary purpose of extracting crude oil.
    Olefins
    A class of unsaturated aliphatic hydrocarbons having one or more double bonds (e.g. propylene, ethylene), produced by cracking naphtha or other petroleum fractions at high temperatures. Olefins are among the main precursors of petrochemical products including plastics. See also aromatics.
    Onshore – conventional
    Extraction and preparation activities for the extraction of natural gas and oil, taking place onshore for conventional fossil fuels. In energy statistics, includes onshore conventional natural gas, crude oil and its condensates. See also onshore – unconventional.
    Onshore – unconventional
    Extraction and preparation activities for the extraction of natural gas and oil, taking place onshore for unconventional fossil fuels. In energy statistics, includes onshore unconventional natural gas and oil. Includes oil sands, extra heavy oil, gas-to-liquids, coal-to-gas and coal-to-liquids. See also onshore – conventional.
    Onshore wind
    A type of wind energy, usually electricity, produced by wind turbines installed on land. See also offshore wind.
    Open interest
    In oil trade, the number of unclosed or unfilled contracts, on one side of the market. In any one delivery month, the short interest always equals the long interest, since the total number of contracts sold must equal the total number bought.
    Open-cycle gas turbine (OCGT)
    A type of power plant that operates with only one thermodynamic cycle involving a gas turbine, such as an aeroderivative gas turbine. Relatively cheap to build and can start very quickly, but has relatively low efficiency (33-43% at maximum load, can be significantly lower at part load) and so is often only run for a small number of hours per day when peak power prices exceed operating costs. Size varies, generally in the 5-50 MW range. Sometimes called a simple cycle gas turbine. See also combined-cycle gas turbine.
    Operating capacity
    In the oil sector, this is the amount of refinery capacity that is available for immediate use (including spare capacity and capacity under active repair).
    Option-adjusted spread
    The calculated spread between a computed index of all bonds in a given rating category and its risk-free counterpart.
    Order book
    In the oil sector, the list of tankers currently on order to be built.
    Organic Rankine cycle
    A thermodynamic cycle that is a variation of the Rankine cycle and is used to generate electricity from relatively low-temperature heat. ORC generators use organic, high-molecular-mass working fluids with vaporisation temperatures lower than that of water. Most commonly used for waste heat recovery, co-generation, solar thermal energy and geothermal power.
    Organisation for Economic Co-operation and Development (OECD)
    An intergovernmental organisation. https://www.oecd.org/about/
    Organisation of the Petroleum Exporting Countries (OPEC)
    Formed in September 1960. Its current 13 members are Algeria, Angola, Equatorial Guinea, Gabon, Iran, Iraq, Kuwait, Libya, Nigeria, the Republic of the Congo, Saudi Arabia, the United Arab Emirates and Venezuela. Ecuador suspended its membership in December 1992, rejoined OPEC in October 2007, but decided to withdraw its membership effective 1 January 2020. Indonesia suspended its membership in January 2009, reactivated it again in January 2016, but decided to suspend its membership once again on 30 November 2016. Gabon terminated its membership in January 1995. However, it rejoined in July 2016. Qatar terminated its membership on 1 January 2019. Production from the Saudi-Kuwaiti Neutral Zone may be reported separately, but in reality is shared 50/50 between them and included in respective OPEC quotas.
    Original equipment manufacturer
    The manufacturer of the original components in a finished product, not the aftermarket replacement parts. The term is used differently in different sectors and sometimes refers to manufacturers that make products to be sold under a client's brand name, for example computers. In the automotive sector it usually refers to the makers of the original vehicle’s parts, and the major global OEMs are also the companies behind the highest-profile brand names.
    Orimulsion
    A proprietary boiler fuel produced in Venezuela. It is a 70:30 mixture, or emulsion, of bitumen from the Orinoco belt and water, with small amounts of surfactant. Was hitherto included in OPEC non-conventional oil supply, but production is believed to have ceased from early 2007.
    Other bituminous coal
    Coal used for steam raising purposes and includes all bituminous coal that is not included under coking coal nor anthracite. It has a higher volatile matter than anthracite (more than 10%) and lower carbon content (less than 90% fixed carbon). Its gross calorific value is greater than 23 865 kJ/kg (5 700 kcal/kg) on an ash-free but moist basis.
    Other energy sector
    Covers the use of energy by transformation industries and the energy losses in converting primary energy into a form that can be used in the final consuming sectors. It includes losses in low-emissions hydrogen and hydrogen-based fuels production, bioenergy processing, gas works, petroleum refineries, and coal and gas transformation and liquefaction. It also includes energy own use in coal mines, in oil and gas extraction and in electricity and heat production. Transfers and statistical differences are also included in this category. Fuel transformation in blast furnaces and coke ovens are not accounted for in the other energy sector category.
    Other industry
    Includes light industry and non-specified industry.
    Oxy-combustion
    See oxyfuel combustion.
    Oxy-fuel combustion
    See oxyfuel combustion.
    Oxyfuel combustion
    Burning of a fuel in nearly pure oxygen instead of air. As almost all the nitrogen is removed from the air before combustion, the flue gas stream is lower in volume and high in CO2 content (around 70% by volume), which reduces the production of NOX pollutants, simplifies the removal of sulphur and other contaminants, and significantly lowers the cost of CO2 capture. Oxyfuel combustion systems with CO2 capture include an air separation unit, a boiler and CO2 purification and compression. As of 2023, the largest power plant projects are around 30 MW and pilots for cement kilns are in planning. Also called oxy-fuel combustion and oxy-combustion.
    Oxygenates
    A type of additive for oil. Includes alcohols (methanol, ethanol), ethers such as methyl tertiary butyl ether (MTBE), ethyl tertiary butyl ether (ETBE) and tertiary amyl methyl ether (TAME).

  • P

    Panamax
    Oil tankers between 50 000 and 74 999 deadweight tons. Originally named as a result of being the largest vessels able to transit the Panama Canal, Panamaxes can carry clean or dirty cargoes, depending on the vessel or trade route. They transport, for example, Arabian Gulf exports to Asia and product trade between North Europe and the Mediterranean. See also Aframax.
    Parabolic dish
    A design of concentrating solar power. Large dish-shaped parabolic mirrors concentrate the sunlight on a receiver. Parabolic dish systems can reach very high temperatures above 1 800 K. They are usually between 3 kW and 25 kW in size and are rarely combined together in a solar field, unlike other forms of concentrating solar power such as parabolic trough systems.
    Parabolic trough
    A design of concentrating solar power. Large cylindrical parabolic mirrors concentrate the sunlight on a line of focus. Several of these collectors in a row form a solar field. In most cases, a molten salt is used to transport the heat to a turbine for power generation and can also be used to provide some hours of energy storage before power generation.
    Paraffin waxes
    Residues extracted when dewaxing lubricant oils. The waxes have a crystalline structure that varies in fineness according to the grade, and are colourless, odourless and translucent, with a melting point above 45 °C.
    Paris Agreement
    An agreement within the United Nations Framework Convention on Climate Change ratified by almost 190 countries to tackle climate change. Aims to strengthen the global response to keep a global temperature rise this century well below 2 °C above pre-industrial levels. All parties to the agreement are required to put forward their best efforts through nationally determined contributions and to strengthen their efforts in the years ahead. https://unfccc.int/process-and-meetings/the-paris-agreement
    Partial oxidation
    A means of producing hydrogen from natural gas by reacting it in the presence of a limited amount of oxygen to produce synthesis gas (syngas), which is subsequently upgraded to increase the hydrogen yield and thereby maximise the carbon dioxide available for capture. Originally designed for syngas production, it is less efficient for unabated hydrogen production than steam methane reforming (SMR) or autothermal reforming (ATR) approaches. However, the relative ease of reaching very high levels of CO2 capture, up to 99%, can make it more attractive for producing low-emissions hydrogen once the full costs of CO2 abatement are included. The process is typically much faster than steam reforming and requires a smaller reactor vessel.
    Particular matter
    Particles of solids or liquids that are in the air. Includes PM2.5 and PM10
    Parts per million (PPM)
    A measurement of the concentration of a gas in a mixture of gases. Usually used for pollution in air and CO2 in the atmosphere. In 2022 global average CO2 concentration in the atmosphere reached around 417 parts per million, more than 50% above pre-industrial levels.
    Passenger kilometre (pkm)
    An indicator of demand for travel, measured as the number of kilometres travelled per passenger over a fixed period such as a year. Used in the calculation of energy efficiency indicators and to project future travel demand. See also tonne kilometre.
    Passenger light-duty vehicle (PLDV)
    A vehicle classification that includes four-wheeled passenger cars. In general, pick-up trucks are included in the separate category of light commercial vehicles.
    Passive solar
    A technique most commonly used in building design that takes advantage of aspect, climate and materials to minimise energy use (including energy derived from solar PV or other on-site renewable energy sources) for lighting, heating and cooling. The main elements of passive solar include: window design and orientation; the thermal mass of the walls and roof; convection or radiation to move warmth within the building; and controls, such as shutters, blinds, overhangs, vents or fans. In energy statistics, passive solar is not included within solar energy.
    Patent fuel
    A composition fuel made by moulding hard coal fines into briquette shapes with the addition of a binding agent.
    Peak demand
    The highest energy demand that has occurred over a specified time on a network, such as demand for electricity from a power network.
    Peak load
    A term for peak demand in the electricity sector.
    Peat
    A solid formed from the partial decomposition of dead vegetation under conditions of high humidity and limited air access (initial stage of coalification). It is available in two forms for use as a fuel, sod peat and milled peat.
    Peat briquettes
    A fuel comprising small blocks of dried, highly compressed peat made without a binding agent.
    Peat products
    This division includes products such as peat briquettes derived directly or indirectly from sod peat and milled peat.
    Pebble-bed reactor
    A type of nuclear fusion reactor that is graphite-moderated and gas-cooled. Operates at very high temperatures and has spherical fuel elements made of graphite surrounding particles of uranium. Designed to have high efficiency and inherent safety features that would prevent meltdown in the event of high-temperature accidents. While originally suggested in the United States in the 1940s and piloted in Germany in in the 1980s, the only operational plants as of 2023 are in China, where two 211 MW reactors were commissioned in 2021.
    Performance-based payment
    A type of support policy in the category of payments and transfers. Seeks to encourage certain activities by making funds available in a way that is directly linked to the quantity (and, potentially, quality) of the output or result of the activity, such as the generation of renewable electricity or storage of CO2.
    Petrochemical
    A chemical product derived from a process that converts hydrocarbon feedstock (usually petroleum products from crude oil refining or natural gas liquids). Includes organic chemicals, intermediate compounds and finished products such as plastics, fibres, solvents and surfactants.
    Petroleum
    A complex mixture of hydrocarbons occurring in liquid, gaseous and solid form, most often conceived of in its liquid form and commonly called crude oil. See crude oil.
    Petroleum coke
    A black solid obtained mainly by cracking and carbonising heavy hydrocarbon oils, tars and pitches. It consists mainly of carbon (90-95%) and has a low ash content. The two most important categories are green coke and calcined coke.
    Petroleum products
    See oil product.
    Petroleum waxes
    Waxes from petroleum sources. Includes paraffin wax and microcrystalline wax from petroleum sources.
    Phase change material
    Substances that absorb and release heat energy when they change phase, such as when they melt from a solid to a liquid, freeze from a liquid to a solid or vaporise from a liquid to a gas. This energy is known as latent heat, and thermal energy storage in phase change materials is known as latent heat storage. It is generally more efficient than thermal energy storage in materials that do not change phase but change temperature instead, which is called sensible heat storage. Phase change materials include paraffins and salt hydrates.
    Photovoltaic (PV)
    PV cells harness the photovoltaic effect to convert light into electrical energy. Multiple PV cells are combined in PV panels that are manufactured as PV modules for sale and installation. Installation can include a device called a tracker to tilt the PV module and increase the solar incidence during the course of the day. Most solar energy is generated using PV. As of 2023, crystalline polysilicon is the dominant technology for PV modules, with more than 95% market share. Within this category, a shift to more efficient monocrystalline wafers accelerated in the early 2020s, with the technology capturing almost all crystalline PV production. As of 2023, commercial monocrystalline PV has an efficiency of around 15-23%.
    Physical delivery
    Supplying or taking delivery of a commodity at an agreed price and location.
    Plant condensate
    A natural gas liquid, mostly low-boiling paraffinic hydrocarbons and heavier hydrocarbons, recovered and separated as liquids at gas inlet separators or scrubbers in processing plants.
    Plastic collection rate
    Proportion of plastics that is collected for recycling relative to the quantity of plastic waste available.
    Plastic waste
    The plastic waste generated by the disposal of plastic consumer products and the plastic fractions of multi-material products that have reached the end of their useful lives.
    Plug-in hybrid electric vehicle (PHEV)
    A type of electric road vehicle that contains both an internal combustion engine and an electric drivetrain with battery pack that can be recharged from an external power source. Usually has a larger battery than a hybrid electric vehicle and a smaller battery than a battery electric vehicle. See also hybrid electric vehicle, battery electric vehicle, fuel cell electric vehicle.
    Plunger
    A device for extracting liquid hydrocarbons more efficiently, while limiting the escape of methane. As pressure from accumulating fluids builds up, it pushes on the plunger. The plunger draws up gas and liquids in its wake. If a certain threshold of reservoir pressure is achieved through withdrawal of the plunger, gas can go directly to the sales line with no venting. Plungers are used to avoid the need to open wells to vent methane to relieve pressure when downhole liquids need to be periodically removed to facilitate continued flow of product. See also liquids unloading.
    Plunger lift
    See plunger.
    PM10
    Inhalable particulate matter with a diameter of 10 microns or less. Airborne particulate matter is not a single pollutant but a complex mixture of solid and aerosol chemical species. For air quality regulatory purposes, pollutant particles are defined by their diameter. PM10 pollution found in outdoor air comes from the combustion of gasoline, oil, diesel fuel and wood, plus dust from construction sites, landfills and agriculture, wildfires and waste burning, industrial sources, wind-blown dust from open lands, pollen and fragments of bacteria. See also PM2.5.
    PM2.5
    Fine particulate matter with a diameter of 2.5 microns or less. Airborne particulate matter is not a single pollutant but a complex mixture of solid and aerosol chemical species. For air quality regulatory purposes, pollutant particles are defined by their diameter. Much of the PM2.5 pollution found in outdoor air comes from the combustion of gasoline, oil, diesel fuel and wood. See also PM10.
    Power
    The amount of energy transferred or converted per unit of time. In the International System of Units, the unit of power is the watt, equal to one joule per second. The capacity of energy infrastructure is rated using watts, which indicate its potential to supply or consume energy in a given period of time. A power plant rated at 100 MW has the potential to produce 100 MWh if it operates for one hour.
    Power generation
    Refers to electricity generation and heat production from all sources of electricity, including electricity-only power plants, heat plants, and co-generation (i.e. combined heat and power) plants. Both main activity producer plants and small plants that produce fuel for their own use (auto-producers) are included.
    Power system inertia
    The energy stored in large rotating generators (such as the generators of thermal electricity generating plants) and some industrial motors, which gives them the tendency to remain rotating. This stored energy can be particularly valuable when a large power plant connected to the same grid fails, as it can temporarily make up for the power lost from the failed generator. This temporary response, which is typically available for a few seconds, allows the mechanical systems that control most power plants time to detect and respond to the failure. Historically, inertia from conventional fossil, nuclear and hydropower generators was abundant. However, as the grid evolves with increasing penetration of asynchronous generators, such as wind, solar photovoltaics and battery storage, that do not inherently provide inertia, questions have emerged about the need for inertia and its role in the future grid.
    Pressurised heavy water reactor
    A nuclear fission reactor that uses heavy water as its coolant and neutron moderator. The main designs are known as CANDU (Canada deuterium uranium) and use a deuterium oxide (heavy water) moderator. The high cost of the heavy water is offset by the avoided cost of enriched uranium fuel or more complex fuel cycles. Uses a closed primary circulation loop to transport heat via liquid heavy water to a second closed loop in which steam is the working fluid for powering the turbine to generate electricity. As of 2020, operational plants totalled 23.9 GW (7% of the installed nuclear fleet worldwide).
    Pressurised water reactor
    A nuclear fission reactor in which water under high pressure is used as a coolant that is heated in the reactor core and transfers its heat to a secondary water system in which steam is generated to power a turbine. As of 2020, operational plants totalled 287.1 GW (73% of the installed nuclear fleet worldwide).
    Primary energy supply
    Energy production plus energy imports, minus energy exports, minus international bunkers, then plus or minus stock changes.
    Primary recovery
    Oil produced by the natural pressure in the reservoir.
    Primary solid biofuels
    See solid bioenergy.
    Primary stocks
    Primary stocks include stocks held in refineries, natural gas processing plants, oil terminals and entrepôts (where these are known), pipelines and stocks held on board incoming ocean vessels in port or at mooring. They exclude power station stocks (since demand is reported as deliveries from primary stocks). They are on a national territory basis, i.e. they include all primary stocks within the national boundaries regardless of ownership (stocks held abroad by government or companies are thus excluded). Note that stocks prior to 1 January 1991 are reported on an ownership basis.
    Process emissions
    CO2 emissions produced from industrial processes other than combustion that chemically or physically transform materials. A notable example is cement production, in which CO2 is emitted when calcium carbonate is transformed into lime, which in turn is used to produce clinker. Includes emissions from lime production for cement, coke oxidation for iron ore reduction and some petrochemical processes.
    Processing gain
    The volume by which total oil refinery output is greater than input for a given period of time. This difference is due to the processing of crude oil into products, which, in total, have a lower specific gravity than the crude oil and feedstocks processed (e.g. in conversion processes).
    Production subsidy
    When applied to fossil fuels, this is a financial incentive (such as a tax reduction on exploration, extraction or sales) that encourages the production of a resource, such as oil or natural gas, above the level that would have been economically attractive without the subsidy. Policy measures that encourage production of an energy source (such as renewable energy whose externality benefits are not valued by the market) by guaranteeing payments in proportion to the level of output are generally referred to as performance-based payments, and include feed-in-tariffs, feed-in-premiums and contracts-for-difference. See also consumption subsidy.
    Productive uses
    Energy used towards an economic purpose: agriculture, industry, services and non-energy use. Some energy demand from the transport sector, e.g. freight, could be considered as productive, but is treated separately.
    Propane dehydrogenation
    A process that converts propane (a component of liquefied petroleum gas) to propylene, which is used commonly in various petrochemical applications. An attractive process for regions that have cheaper light feedstock availability and its potential to produce hydrogen as a by-product, it is complex to implement owing to various side reactions. As of 2023, fewer than 50 plants are operational worldwide, mostly in China, where capacity is expanding rapidly.
    Proton exchange membrane electrolyser
    A type of water electrolyser system for making hydrogen with electricity. Uses pure water as an electrolyte solution, and so avoids the recovery and recycling of the potassium hydroxide electrolyte solution that is necessary with alkaline electrolysers. Operating range can go from zero load to 160% of design capacity (so it is possible to overload the electrolyser for some time, if the plant and power electronics have been designed accordingly). However, needs expensive electrode catalysts (platinum, iridium) and membrane materials, and, as of 2023, lifetime is shorter and overall costs are generally higher than those of alkaline electrolyser, and so far less widely deployed. See also alkaline electrolysis and solid oxide electrolyser cell.
    Proved
    In the oil and gas sector, proved reserves are estimated quantities of crude oil, condensates and natural gas liquids that geological and engineering data demonstrate with “reasonable certainty”(80-90% confidence) to be recoverable in future years by specified techniques (where the development scenario has been defined and known technology is used) and which are commercial under current economic conditions (prices and costs prevailing at the time of the evaluation). See also proved plus probable and proved plus probable plus possible.
    Proved plus probable
    Oil and gas reserve estimates based on median estimates of the accumulation that are more likely to be recovered than not (50% confidence). This can result from either better reservoir behaviour than expected under the proved category or additional investment to be decided over the medium to long term (three to ten years) using conventional techniques with possible economic uncertainties. See also proved and proved plus probable plus possible.
    Proved plus probable plus possible
    Oil and gas reserve estimates based on a maximum estimate of the accumulation with maximum recovery factors without economic considerations (10-20% confidence). See also proved and proved plus probable.
    Proven
    See proved.
    Pulverised coal (PC)
    A type of processed coal that is fed into a pulverised coal combustion system. Made by crushing coal to a powder with grains of less than 0.1 mm, for example by using cylindrical grinding rollers and heating to remove moisture. Burns more quickly than non-pulverised coal and can be easily blown into a boiler.
    Pulverised coal combustion (PCC)
    A technology for burning coal that involves injecting pulverised coal into a furnace in the presence of a controlled level of air. Most coal-fired power plants are PCC plants that use steam to drive a steam turbine. Includes subcritical, supercritical steam and ultra-supercritical steam plants. See also integrated gasification combined cycle, direct injection coal engine and oxyfuel coal plants.
    Pumped storage
    See pumped-storage hydropower.
    Pumped-storage hydropower
    A form of electricity storage by which electrical energy is converted to potential energy by pumping water to a reservoir at higher elevation, from which it can be passed through a turbine to generate electricity at a future time. As of 2023, PSH represents the largest installed type of electricity storage globally. Originally installed to shift demand to match inflexible electricity generators, such as nuclear power plants, with more variable daily demand, PSH is increasingly used to shift variable electricity supplies, such as solar and wind, temporally. Some PSH systems are integrated into reservoir hydropower systems that are also fed by river water.

  • R

    Rare earth elements
    A group of 17 chemical elements in the periodic table, specifically the 15 lanthanides plus scandium and yttrium. Key components in some clean energy technologies, including wind turbines, electric vehicle motors and electrolysers.
    Rare earths
    See rare earth elements.
    Reaktor bolshoy moshchnosti kanalnyy
    A water-cooled nuclear fission reactor that uses enriched uranium as its fuel and graphite as a moderator. Designed in the Soviet Union in the 1960s with the potential for plutonium production as well as energy supply. The Chernobyl nuclear power plant is an RBMK design. The youngest RBMK entered operation in 1990.
    Refined oil product
    See oil product.
    Refined product
    See oil product.
    Refinery
    An installation with the primary function of making oil products from crude oil, unfinished oils, natural gas liquids, other hydrocarbons, oxygenates, additives and hydrogen. Includes topping refinery, hydroskimming refinery and complex refinery.
    Refinery feedstocks
    Oils and gases from crude oil refining or the processing of hydrocarbons in the petrochemical industry that are destined for further processing in the refinery, excluding blending. Typical feedstocks include naphtha, middle distillates, pyrolysis gasoline and heavy oils from vacuum distillation and petrochemical plants.
    Refinery gas
    A mixture of non-condensable gases, mainly consisting of hydrogen, methane, ethane and olefins, obtained during the distillation of crude oil or treatment of oil products (e.g. cracking) in refineries or from nearby petrochemical plants.
    Refinery yield
    A measure of refinery efficiency defined as the finished product as a percentage of the input of crude oil and the net input of feedstock. It is calculated by dividing total net production volume of finished oil products by the sum of crude oil volume and net unfinished input volume.
    Refining margin
    The net difference in value between the products produced by a refinery and the cost, insurance and freight value of the crude oil used to produce them, taking into account the marginal refinery operating costs. Refining margins vary from refinery to refinery and depend on the cost and characteristics of the crude used, its yield and the value of its products (and hence its location).
    Reforming
    An oil refining process using controlled heat and pressure with catalysts to rearrange hydrocarbon molecules in the naphtha (or naphtha-type) feed, thereby converting paraffinic and naphthenic type hydrocarbons (low octane gasoline boiling range fractions) into higher octane stocks suitable for blending into finished gasoline. Since the product of the process, reformate, is richer in aromatics than its feed, naphtha, this process is also used to produce aromatic petrochemical building blocks (benzene, toluene and xylene).
    Reformulated blendstock for oxygenate blending
    Unfinished gasoline that is made ready to be blended with ethanol to make reformulated gasoline. The addition of ethanol reduces knocking and smog formation, but it is generally only possible close to the point of sale, which explains why RBOB is a widely traded product. If the ethanol is 10% by volume, the reformulated gasoline is E10. See also conventional blendstock for oxygenate blending, which is similar to RBOB, but has less strict environmental specifications.
    Reformulated gasoline
    Finished motor gasoline that meets the requirements of the reformulated gasoline regulations of the US Environmental Protection Agency under Section 211(k) of the Clean Air Act.
    Refrigerant
    Heat transfer fluids used in vapour-compression refrigeration cycles in refrigerators, air conditioners and heat pumps. Characterised by low boiling point and high heat capacity, which enables the refrigerant to transfer a large amount of heat very efficiently.
    Regasification
    The process of converting a liquefied gaseous fuel back to gaseous state by heating. Usually refers to the regasification step of the liquefied natural gas value chain, but could also apply to other gaseous fuels, including hydrogen. See also liquefaction.
    Regasification terminal
    A facility, usually at a sea port, for regasification of shipped liquefied gaseous fuels such as liquefied natural gas or, potentially, hydrogen.
    Regulated entity
    In energy markets, licensees whose activities are governed by a set of rules designed to ensure the provision of public services without exploitation of a natural monopoly position. In electricity and natural gas supply, can include generators, transmitters, distributors, storage companies, retailers, wholesalers, distribution system operators (DSOs) and transmission system operators (TSOs), depending on the market structure. Key activities that are subject to regulatory approval include infrastructure investment (for DSOs and TSOs) and tariff-setting (for integrated utilities active in retail as well as supply, distribution and transmission).
    Reid vapour pressure
    A measure of the ease with which gasoline evaporates. While gasoline must be in a vapour form to ignite, insufficient or excess volatility has adverse consequences. Gasoline typically has different volatility levels depending on the time of year and the associated average ambient temperature. Summer grade gasoline needs to be less volatile than winter grade, allowing less evaporation than would otherwise be the case. Insufficiently volatile gasoline can lead to poor cold-start properties, while excess volatility can cause vapour lock and excess emissions. The RVP refers to the amount of pressure that the gasoline can generate under test conditions.
    Renewable energy sources (RES)
    See renewables.
    Renewable natural gas
    See biomethane.
    Renewable portfolio standard
    See renewable/non-fossil energy obligations
    Renewable/non-fossil energy obligations
    A type of policy support measure to incentivise investment in energy sources with low emissions. Obligated parties, such as electricity retailers, have a legal obligation to procure a rising share of their supply from a specific type of source, such as renewables. Most obligation systems facilitate trading of certificates so that obligated parties can meet their obligation at lowest overall costs. Some systems encourage investment in less mature options with a scale of certificate values that reflects a range of different costs at the time of policy design.
    Renewables
    Includes modern bioenergy, geothermal, hydropower, solar photovoltaics, concentrating solar power, wind, marine (tide and wave) energy, and renewable waste.
    Research octane number
    See octane number.
    Reserves
    In the oil and gas sector, the amount of crude oil, condensates and natural gas liquids that can be technically recovered at a cost that is financially feasible at the present price of oil. Includes proved reserves (1P), proved plus probable reserves (2P) and proved plus probable plus possible reserves (3P)
    Residential
    In energy statistics, the energy used by households for space heating and cooling, water heating, lighting, appliances, electronic devices and cooking.
    Residual fuel oil
    Includes all residual (heavy) fuel oils (including those obtained by blending). One of the lowest-value oil products from a refinery. Kinematic viscosity is above 10 cSt at 80 °C. The flash point is always above 50 °C and density is generally more than 0.90 kg/l. The average specific energy of residual fuel oil is 41 MJ/kg higher heating value.
    Residue
    In oil refining, this includes atmospheric residue, vacuum residue and cracked residue.
    Resource push
    Policies that increase the provision of inputs into the energy innovation system with the intention of raising the chance of innovation success. The two main resources are funding and human capital. For clean energy technology innovation, governments may provide direct funding (e.g. multiannual R&D projects or grants) or indirect funding (e.g. tax breaks for business R&D), targeted to a specific innovation gap or technology neutral, in the earlier stages of R&D. In the intermediate stages of development such as demonstration, emerging technologies may face challenges mobilising much larger capital sums and the public sector can provide financial support (e.g. grants, loans or equity) to mitigate the higher risks associated with this so-called “valley of death”. Policies directed towards human capital use training, education, wages or taxes to increase the supply or quality of inventors, researchers, R&D support personnel, graduates, entrepreneurs, financiers and industry actors. See also market pull, socio-economic support and knowledge management. For policies that primarily push the production of a technology, rather than innovation, see technology push.
    Road transport
    In IEA analysis, this refers to all road vehicle types (passenger cars, two/three-wheelers, light commercial vehicles, buses and medium and heavy freight trucks).
    Run-of-river hydropower
    A type of hydropower electricity generation that uses little or no water storage and does not materially alter the normal course of the river. Depending on definitions, which vary around the world, it can include the use of turbines or buoys to extract only the kinetic energy in the water flow and also the use of systems that use small dams to create a headpond that provides storage of potential energy (up to around 24 hours of generating capacity) and a steady low into the turbine. However, the latter is sometimes called pondage hydropower and classified separately. Most run-of-river systems are much smaller than traditional reservoir hydropower systems, but can be of a similar scale. Run-of-river hydropower can be developed with relatively minimal environmental impacts with appropriate measures to cater for the movements of fish and other animals.
    Run-of-the-river hydro
    See run-of-river hydro.

  • S

    Satellite field
    A separate accumulation of oil onshore or offshore tied back to a central processing facility.
    Scope 1 emissions
    Greenhouse gas emissions that come directly from company operations. See also scope 2 emissions, scope 3 emissions and CO2 intensity.
    Scope 2 emissions
    Greenhouse gas emissions that arise from the generation of energy purchased by companies. See also scope 1 emissions, scope 3 emissions and CO2 intensity.
    Scope 3 emissions
    Greenhouse gas emissions that occur during the use of a company's products, which are more challenging to estimate. See also, scope 1 emissions, scope 2 emissions and CO2 intensity.
    Seasonal coefficient of performance
    Describes the average coefficient of performance of a heat pump during a heating season. Some definitions may include other parts of the heating system than the heat pump only. For cooling and air conditioning applications the seasonal energy efficiency ratio is normally used.
    Seasonal energy efficiency ratio (SEER)
    A measurement of air conditioner efficiency. Calculated as the cooling output during a typical cooling season divided by the total electric energy input during the same period. In the United States, British thermal units are used for cooling output and watt hours for electric input. In Europe, the European seasonal energy efficiency ratio is used. See also coefficient of performance, seasonal coefficient of performance and European seasonal energy efficiency ratio.
    Second-generation biofuels
    See novel advanced biofuels.
    Secondary recovery
    Methods of increasing the percentage of oil recovered from oil fields using natural gas or water injection. Sometimes initiated in parallel with primary recovery. See also primary recovery and tertiary recovery.
    Secondary stocks
    Oil stocks held by power stations, minor bulk plants and wholesalers.
    Security of supply
    See energy security.
    Selective catalytic reduction (SCR)
    A means of reducing nitrogen oxide emissions from combustion. Ammonia or urea are added to the flue gas with a catalyst. In the case of urea, nitrogen and CO2 are produced and emitted. While originally developed for large boilers, it is now applied to diesel engines, including on ships and in cars.
    Self-sufficiency
    In IEA analysis, this is a measure of whether a country would be able to cover its consumption of a fuel by only using its own production. Presented as a percentage and calculated by dividing indigenous production by total energy supply.
    Sewage sludge gas
    A type of biogas produced from the anaerobic fermentation of sewage sludge.
    Shale gas
    A type of unconventional natural gas contained within a commonly occurring rock classified as shale. Shale formations are characterised by low permeability, with more limited ability for gas to flow through the rock than is the case within a conventional reservoir. Shale gas is generally produced using hydraulic fracturing. See also tight oil.
    Shale oil
    An unconventional oil extracted from oil shale by pyrolysis, hydrogenation or thermal dissolution. Needs to be upgraded, for example by hydrogenation, to make an acceptable refinery feedstock. One of the first sources of petroleum oil to have been used by humankind as a fuel.
    Short position
    Created when a trader sells a security with the intention of repurchasing it or covering it later at a lower price. Short-sellers of oil futures profit from falls in the market price of oil, but make losses if the price rises.
    Short ton
    See short tonne.
    Short tonne (st)
    A unit of mass that is not part of the International System of Units. Still commonly used in the United States, abbreviated to "ton". Equal to 0.90718 tonnes. See also long ton.
    Sidetracking
    In upstream oil and gas, use of an existing well bore to drill an additional bore laterally.
    Single-use plastic
    Plastic items used only one time before disposal.
    Small hydro
    See small hydropower.
    Small hydropower
    A type of hydropower generation facility. In IEA analysis, small hydropower has a capacity of less than 10 MW and more than 0.1 MW. See also large hydropower and micro hydropower.
    Small modular reactor
    Advanced nuclear fission reactors that have a power capacity of up to 300 MWe per unit, which is about one-third of the generating capacity of traditional nuclear power reactors. These units can be stacked to create a medium-size power plant or can comprise a single large unit, the largest that can be constructed offsite. The reactors can use existing or new nuclear technologies.
    Smart grid
    A term is used to indicate a desirable future configuration of an electricity network that uses digital and other advanced technologies to monitor and manage the transport of electricity from all generation sources to meet the varying electricity demands of end users. It would coordinate the needs and capabilities of all generators, grid operators, end users and electricity market stakeholders to operate all parts of the system as efficiently as possible, minimising costs and environmental impacts while maximising system reliability, resilience and stability.
    Smart meter
    A device for measuring electricity consumption or generation, or both. Typically includes functions for remote reading, two-way communication, support for variable tariffs and payment systems, and remote disablement and enablement of supply. Usually considered to be a core technology to enable more efficient (or smart) grid infrastructure and power markets. Sometimes has the capability to provide consumers with real-time information about consumption by communicating via data protocols accessible to consumers' networked devices.
    Socio-political support
    Technology innovation-related policies that support a broad range of actors to ease the path of new ideas to emerge and reach markets. Governments can mobilise actors to support or oppose the direction or outcomes of innovation via measures including public communication, stakeholder engagement, funding of expert groups or compensation for perceived losers from the success of a new technology. See also knowledge management, market pull and resource push.
    Solar
    See solar energy.
    Solar energy
    Includes solar photovoltaic, concentrating solar power and solar heating and cooling. Energy statistics do not include passive solar energy.
    Solar heating and cooling
    A type of solar energy involving the harnessing of solar energy for local heating and cooling purposes. Includes solar heat collectors; hot water preparation; combined space heating; active solar heating and cooling; passive solar heating and cooling; solar architecture; solar drying; solar-assisted ventilation; swimming pool heating; and low-temperature process heating. See also passive solar and concentrating solar power.
    Solar home system
    Small-scale photovoltaic and battery stand-alone systems, i.e. with capacity higher or equal to 10 watt peak (Wp) supplying electricity for single households or small businesses. They are most often used off-grid, but also where grid supply is not reliable. Although all SHS are included in the IEA access to electricity definition and historic counting, only solar home systems from 25 Wp in rural areas and 50 Wp in urban areas are deployed in the IEA scenarios for population gaining access. It excludes solar systems smaller than 10 Wp, i.e. multi light systems and solar lanterns.
    Solar photovoltaics
    Electricity produced from solar photovoltaic cells including utility-scale and small-scale installations. See photovoltaic.
    Solid bioenergy
    Includes charcoal, fuelwood, dung, agricultural residues, wood waste and other solid biogenic wastes.
    Solid biomass
    See solid bioenergy.
    Solid fuels
    Includes coal, modern solid bioenergy, traditional use of biomass and industrial and municipal wastes.
    Solid oxide electrolyser cell
    An electrolyser cell that uses ceramics as the electrolyte and has low material costs. Operates at high temperatures and with a high degree of electrical efficiency. As it uses steam for electrolysis, it needs a heat source. The least developed electrolysis technology. Not yet commercialised, although individual companies are now aiming to bring it to market. Can be operated in reverse mode as a fuel cell, converting hydrogen back into electricity, and thus able to provide balancing services to the grid in combination with hydrogen storage facilities.
    Solid oxide fuel cell (SOFC)
    A fuel cell with a solid oxide material as the electrolyte, such as yttria-stabilised zirconia. Produces electricity and water from a fuel input, and can also produce heat or cooling. Can run on hydrogen, although high operating temperatures (500-1 000 °C) mean that light hydrocarbon fuels, such as methane, propane or butane, can be used because they are internally reformed to hydrogen and syngas within the anode. Has high efficiencies of heat and power production. See also proton exchange membrane, solid oxide electrolyser cell, molten carbonate fuel cell.
    Sour crude
    Crude oil with a sulphur content of 1-2% by mass. See also API gravity, sweet crude and total acid number.
    Space cooling
    Any means of lowering indoor temperatures, including air conditioning.
    Space heating
    Any means of raising indoor temperatures, including central heating, district heating, passive solar, air-to-air heat pumps and storage heaters among others.
    Special boiling point industrial spirit
    See industrial spirit
    Specific energy
    Energy per unit mass. Sometimes called gravimetric energy density.
    Specific gravity
    The mass per unit volume of a substance such as oil, relative to the density of water, which has a specific gravity of 1.0. Most oils lie in the range of 0.6-1.0. The lower the specific gravity, the lighter the oil.
    Spot month
    In oil trade, this is the nearest deliverable month.
    Spot price
    The current bid or offering price for a crude oil or product, for immediate delivery.
    Spot trade
    A one-time open market transaction where physical products are traded at current market rates. In oil trade, the term is also often used to refer to a front-month futures contract.
    Spudding
    In upstream oil and gas, this is the initial drilling of a well.
    Squeeze
    In oil trade, this occurs when traders are forced to cover their positions by a change in technical or fundamental conditions or the pending expiry of a commodity. Frequently occurs when sellers of a commodity do not have the physical material to deliver against a contract and are forced to close out positions with (a limited number of) buyers waiting to receive delivery. Such market behaviour often occurs when a market is in short supply, but can also occur close to the expiry of a contract when time constraints may limit the ability of a player to conduct a physical transaction. Bull squeezes, where prices are forced higher are most frequently noted, but bear squeezes, where buyers of paper contracts do not wish to take physical delivery, can also occur. Deliberate manipulation of futures markets is outlawed by most exchanges, who take action if inappropriate market behaviour is noted.
    Stand-alone systems
    Small-scale autonomous electricity supply for households or small businesses. They are generally used off-grid, but also where grid supply is not reliable. Stand-alone systems include solar home systems, small wind or hydro generators, diesel or gasoline generators. The difference compared with mini-grids is in scale and that stand-alone systems do not have a distribution network serving multiple costumers.
    Standard cubic foot (scf)
    A volume of gas contained in one cubic foot of space at a certain reference temperature and pressure. These conditions depend on the type of gas.
    Standard cubic metre
    A volume of gas contained in one cubic metre of space at a temperature of 15.5 °C and pressure of 1.01325 bar (14.695 psi).
    Standing Group for Global Energy Dialogue
    A committee that forms part of the IEA governance structure. It is responsible for work with countries and regions outside the IEA membership, including China and India. Many SGD projects draw upon both regional and sectoral expertise. See also CERT, SEQ, SLT, SOM and CBE. For more information: https://www.iea.org/about/structure.
    Standing Group on Emergency Questions
    A committee that forms part of the IEA governance structure. It is responsible for all aspects of oil emergency preparedness and collective response to supply disruptions. See also CERT, SOM, SLT, SGD and CBE. For more information: https://www.iea.org/about/structure.
    Standing Group on Long Term Co-operation
    A committee that forms part of the IEA governance structure. It encourages co-operation among IEA member countries to ensure collective energy security, improve the economic efficiency of their energy sector and promote environmental protection in provision of energy services. The SLT has also established the Working Party on Energy Efficiency and the Working Party on Critical Minerals. See also SEQ, SOM, CERT, SGD and CBE. For more information: https://www.iea.org/about/structure.
    Standing Group on the Oil Market
    A committee that forms part of the IEA governance structure. It monitors and analyses short- and medium-term developments in the international oil market to help member countries react promptly and effectively market changes. See also CERT, SEQ, SGD, SLT and CBE. For more information: https://www.iea.org/about/structure.
    Stated Policies Scenario (STEPS)
    An IEA scenario that explores one possible future projection of the global energy system by reflecting the impact of existing policy frameworks and announced policy intentions at the time of scenario construction. The aim is to hold up a mirror to the plans of today’s policy makers and illustrate their consequences for energy use, emissions and energy security, and to provide a detailed sense of the direction in which existing policy frameworks and today’s policy ambitions would take the energy sector out to 2040. Previously known as the New Policies Scenario, it was renamed in WEO 2019 to underline that it considers only specific policy initiatives that have already been announced.
    Statistical differences
    In energy statistics, these are discrepancies between reported supply and demand. Includes unexplained statistical differences for individual fuels and statistical differences that arise from the use of inconsistent conversion factors.
    Steam coal
    A type of hard coal used for heat production or steam-raising in power plants and, to a lesser extent, in industry. Typically, steam coal is not of sufficient quality for steel making. Has a specific energy of around 25 MJ/kg on a lower heating value basis. Sometimes called thermal coal or, in energy statistics, other bituminous coal.
    Steam methane reforming
    A means of producing hydrogen from hydrocarbons, especially natural gas. First, methane reacts with steam under pressure in the presence of a catalyst to produce hydrogen, carbon monoxide and carbon dioxide (i.e. synthesis gas). This process requires an external input of heat, which leads to lower efficiencies. Next, a water-gas shift reaction is carried out and the carbon monoxide reacts with steam in the presence of another catalyst to produce carbon dioxide and more hydrogen. Finally, pressure-swing adsorption or another method is used to remove the carbon dioxide and other impurities from the hydrogen.  
    Stimulated geothermal system
    See enhanced geothermal system.
    Straight-run
    A refined oil product of petroleum made by distillation without additional conversion.
    Sub-bituminous coal
    A type of coal that has specific energy between 20 MJ/kg and 24 MJ/kg on a higher heating value basis and contains more than 31% volatile matter on a dry mineral matter-free basis. See also bituminous coal, lignite and hard coal.
    Subcritical
    A designation for fuel combustion facilities that operate at up to 374 °C and pressure levels below 22 MPa, especially coal-fired power plants. Less energy efficient than supercritical plants. Subcritical coal-fired power plants can reach around 33% and 37% lower heating value. See also supercritical and ultra-supercritical.
    Subsea template
    In upstream oil and gas, a frame anchored to the seabed containing one or more well heads. Usually tied back to an existing platform or production vessel.
    Subsidies
    In IEA analysis, a government action directed primarily at the energy sector that lowers the cost of energy production, raises the price received by energy producers or lowers the price paid by energy consumers. See also consumption subsidy.
    Suezmax
    Suezmax vessels are oil tankers between 120 000 and 199 999 deadweight tons. Originally named for being the largest vessels able to transit the Suez Canal, Suezmaxes mostly carry dirty cargoes, especially crude oil, in parcel sizes of 130 000 tonnes (around one million barrels). Typical routes include West African exports to the United States and Europe, North Sea exports to the United States and Europe and some Arabian Gulf exports. See also Aframax, Panamax, Handymax, Handy vessel and very large crude carrier.
    Sulphur dioxide (SO2)
    An inorganic chemical compound that is produced industrially for sulphuric acid and is also a pollutant by-product of fossil fuel combustion. Also a product of volcanic eruptions. Sulphur dioxide emissions deplete ozone and are a precursor to acid rain and atmospheric particulates. Dangerous to human and ecosystem health and have been mitigated substantially since the introduction of flue-gas desulphurisation technologies at coal-fired power plants. SO2 emissions are being further reduced by the shift to low-sulphur fuels for marine transport. However, reducing SO2 emissions can also have a warming effect on the climate as SO2 converts to sulphate aerosols that block incoming solar radiation and nucleate clouds that can also reflect incoming radiation.
    Supercritical (SC)
    A designation for fuel combustion facilities that operate above 374 °C (usually around 566 °C) and pressure levels of 22 MPa, especially coal-fired power plants. They differ from traditional coal power plants because the water running through them works as a supercritical fluid. They are more energy efficient than subcritical plants, but not as energy efficient as ultra-supercritical plants. Supercritical coal-fired power plants can reach around 44% lower heating value efficiency. See also subcritical and ultra-supercritical.
    Supply
    See primary energy supply. In IEA investment analysis, supply includes upstream, midstream and downstream oil and gas, coal mining and distribution, electricity and heat generation, electricity and heat networks (including electricity storage in front of the meter and EV fast chargers), low-emissions hydrogen and low-emissions hydrogen-based fuels production and distribution (except on-site hydrogen production), liquid biofuels production (does not include bioenergy resource cultivation), and other energy sectors (such as coal-to-liquids, gas-to-liquids , coal-to-gas).
    Supply push
    Oil trade that is motivated by output surpluses at the point of origin, often signalled by weakness in local refining margins or by weak relative prices. Also used to characterise a group of policies that seek to raise the deployment of a good or service by directly incentivising more production rather than seeking to act via an increase in demand (and thus an indirect stimulus to production). Examples of supply push policies might include production subsidies or resource auctions. Care must be taken to define the unit of analysis, as a demand pull policy for wind turbines might be a supply push policy for renewable electricity. See also demand pull. For clean energy innovation system push and pull policy measures, see also market pull and resource push.
    Sustainable Development Goal (SDG)
    In 2015 all countries of the world adopted 17 ambitious policy goals to end poverty, protect the planet, promote gender equality and ensure prosperity, as part of the United Nations Sustainable Development Agenda, and vowed to achieve specific targets by 2030. Energy is at the heart of many of them – from expanding access to electricity, to improving clean cooking fuels, from reducing wasteful energy subsidies to curbing deadly air pollution that each year prematurely kills millions around the world. One of these goals – commonly known as SDG7 – aims to ensure access to affordable, reliable, sustainable and modern energy for all by the end of the next decade. The IEA Net Zero Emissions by 2050 Scenario supports emerging market and developing economies to achieve the energy-related SDGs. See: https://sdgs.un.org/goals.
    Sustainable Development Scenario (SDS)
    An IEA scenario that was presented in World Energy Outlook 2017-2021 that sets out the major changes that would be required to reach the key energy-related goals of the United Nations Sustainable Development Agenda (SDGs). These are: an early peak and rapid subsequent reductions in emissions, in line with the Paris Agreement; universal access to modern energy by 2030, including electricity and clean cooking; a dramatic reduction in energy-related air pollution and the associated impacts on public health. The trajectory for emissions in the Sustainable Development Scenario was consistent with reaching global “net zero" CO2 emissions in 2070.
    Sustainable Energy for All
    An international organisation launched in 2011 that works in partnership with the United Nations and leaders in government, the private sector, financial institutions, civil society and philanthropies to drive faster action towards the achievement of Sustainable Development Goal 7 (SDG7) – access to affordable, reliable, sustainable and modern energy for all by 2030 – in line with the Paris Agreement on climate. The annual report on tracking SDG7 is a joint effort of the International Energy Agency, the International Renewable Energy Agency, United Nations Statistics Division, the World Bank and the World Health Organization.
    Sustainable production capacity
    In oil and gas analysis, this is a capacity level that can be reached within 90 days and sustained for an extended period.
    Sweet crude
    Crude oil with a sulphur content of less than 1% by mass. See also sour crude and total acid number.
    Synchronous generator
    A machine that converts mechanical power into alternating-current electric power through the process of electromagnetic induction.
    Synfuel
    See synthetic fuel.
    Syngas
    See synthesis gas.
    Synthesis gas
    Also known as syngas. A gas that is primarily composed of hydrogen and carbon monoxide and produced via gasification, reforming or pyrolysis of solid bioenergy, coal, natural gas or oil. The composition of syngas can vary considerably depending on the fuel source, and this strongly affects the energy content. Formerly, syngas was the main source of town gas, a piped gas used for lighting and cooking made from coal. Today, it is the precursor for a range of chemicals (for example, methanol), hydrogen (for example, via steam methane reforming or coal gasification) and synthetic fuels (for example, coal-to-liquids, gas to liquids and low-emissions hydrogen-based synthetic hydrocarbons). Syngas can be used directly as a gaseous fuel, for example in integrated gasification combined-cycle power plants without carbon capture, utilisation and storage, or in the on-site combustion of blast furnace gas and coke oven gas.
    Synthetic crudes
    A type of crude oil made by upgrading bituminous (e.g. oil sands) or extra-heavy crude oils, increasing their value and making them transportable by pipeline without dilution or heating. Unlike naturally occurring bitumen, synthetic crudes are generally excluded from the definition of conventional crude production in energy statistics. However, in the case of Venezuela, heavy crude feedstock normally destined for upgrading units is now counted towards monthly crude supply, in line with market convention and current OPEC quota considerations. See also synthetic fuels.
    Synthetic fuel
    A fuel, either synthetic liquid fuel or synthetic gaseous fuel, obtained via a process other than the refining of crude oil or bituminous oils. Also known as synfuel.
    Synthetic gaseous fuels
    Gaseous liquid fuels obtained via a process other than the refining of crude oil or bituminous oils, or biomass fermentation or transesterification. Includes gas-to-liquids, synthetic gas and synthetic methane. If produced using low-emissions hydrogen and a sustainable source of carbon, the resulting fuel is included in the set of low-emissions gaseous fuels.
    Synthetic hydrocarbons
    Includes coal-to-gas, gas-to-liquids, coal-to-liquids, synthetic hydrogen-based liquids and synthetic methane.
    Synthetic liquid fuels
    Any liquid fuel obtained via a process other than the refining of crude oil or bituminous oils, or biomass fermentation or transesterification. Most synthetic liquid fuels are produced via synthesis gas production followed by the Fischer-Tropsch synthesis process. Includes coal-to-liquids, gas-to-liquids, thermochemical biomass-to-liquids and low-emissions hydrogen-based liquid fuels.
    Synthetic methane
    Methane from sources other than natural gas, including coal-to-gas and low-emissions synthetic methane.
    Synthetic oil
    Liquid fuels obtained via a process other than the refining of crude oil or bituminous oils. Synthetic oil is produced through Fischer-Tropsch conversion or methanol synthesis. It includes oil products from coal-to-liquids, gas-to-liquids, thermochemical biomass-to-liquids and non-ammonia low-emissions liquid hydrogen-based fuels.

  • T

    Tanker
    Cargo ships fitted with tanks for carrying liquids such as crude oil, liquefied natural gas or oil products in bulk. See Aframax, Panamax, Handymax, Handy vessel, Suezmax and very large crude carrier.
    Tanker fundamentals
    In oil markets, this refers to the supply and demand for oil tankers.
    Tar
    Naturally occurring, viscous and dense hydrocarbons.
    Tar sands
    See oil sands.
    Technicals
    Factors other than fundamental ones which influence futures price development. These could include the breach of a previous price level, changes in open interest, volume, degree of recent price movement, the approach of contract expiry, trend indicators, moving averages, support and resistance lines, and relative strength index. See technical analysis.
    Technology application
    A broad category representing a general energy challenge that technology can help solve, such as low-carbon electricity generation, emissions-free mobility and low-emissions steelmaking. See also: technology type, technology design and technology component.
    Technology Collaboration Programme (IEA)
    IEA TCPs are independent, international groups of experts that enable governments and industries from around the world to lead programmes and projects on a wide range of energy technologies and related issues. The experts in these collaborations work to advance the research, development and commercialisation of specific energy technologies. As of 2023, there are experts from 55 countries involved in 39 TCPs focused on topics across many sectors, including buildings, transport, industry, renewable energy, fossil energy and fusion power. The establishment and continuation of TCPs are based on recommendations from the IEA Committee on Energy Research and Technology (CERT). For more information: https://www.iea.org/areas-of-work/technology-collaboration.
    Technology component
    In the system of technology type, technology design and technology component, components are integral parts that distinguish one design from another, but are not a solution to any energy technology challenges by themselves. For example, a perovskite solar PV module is a technology design for the technology type of solar PV, which fits the technology application of low-carbon electricity generation, and integrates the technology component of hole-transport layer materials.
    Technology design
    In IEA analysis a technology design is a specific technical configuration of a given technology type, generally embodied by a saleable product. Different technology designs may be developed to fit different applications and contexts or may compete with one another for market share. Technology designs may themselves integrate multiple technology components in ways that distinguish each specific design. For example, a perovskite solar PV module is a technology design for the technology type of solar PV, which fits the technology application of low-carbon electricity generation, and integrates the technology component of hole-transport layer materials.
    Technology push
    A type of government policy that aims to increase the supply of a selected technology by incentivising its producers to raise output, thus decreasing prices through economies of scale and induced innovation. Sometimes used to refer to policies that fund technology innovation, including R&D, in a specific technology area as a means of improving the technology's performance and reducing its cost, an approach referred to in IEA analysis as resource push. Often contrasted with demand pull measures.
    Technology Readiness Level
    A measure of how a technology has progressed from initial concept to saleable product with standard performance guarantees. TRLs follow a nine-point scale, originally developed by NASA. The levels used by the IEA are: 1 = initial idea; 2 = application formulated; 3 = concept needs validation; 4 = early prototype; 5 = large prototype; 6 = full prototype at scale; 7 = pre-commercial demonstration; 8 = first-of-a-kind commercial; 9 = commercial operation in relevant environment. The IEA's ETP Clean Energy Technology Guide also uses the levels 10 and 11 to indicate the extent to which a technology has been deployed. The TRL scale is most informative when applied to technology designs, such as perovskite solar PV, or technology components, such as hole-transport layer materials, rather than technology types, such as solar PV in general. IEA modelling scenarios are cautious about reliance on any technology type with no designs at TRL 9.
    Technology type
    In IEA analysis a technology type is a group of similar solutions to an energy challenge (or technology applications). Examples of technology types are: solar PV; geothermal electricity generation; electric vehicle; and heat pump. Each technology type usually has multiple technology designs that fit different market needs or compete with one another for market share. Technology designs may themselves integrate multiple technology components in ways that distinguish each specific design.
    Tertiary recovery
    Methods of increasing the percentage of oil recovery beyond that achieved by secondary recovery. These include injecting solvents or high-pressure carbon dioxide, igniting part of the oil in the reservoir to generate steam, and biological breakdown of oils to enable them to flow more easily.
    Tertiary stocks
    Stocks held by end consumers, including industrial, commercial and private stocks.
    Thermal capacity (th)
    See thermal mass.
    Thermal coal
    See steam coal.
    Thermal cracking
    An oil refining process in which heat and pressure are used to break down, rearrange or combine hydrocarbon molecules. Thermal cracking includes visbreaking, fluid coking, delayed coking and other similar processes.
    Thermal energy storage
    A means of storing heat (or cold) in the form of latent and/or sensible heat with the ability to release it on demand for use later in heating, cooling or, in some cases, power generation. Can include molten salt storage, ice storage, phase change materials, hot water storage or underground thermal energy storage (including pit storage tanks). Commonly paired with concentrating solar power, district heating or cooling and nuclear electricity (e.g. via overnight domestic hot water boilers). Is gaining interest as a source of flexibility for energy transitions.
    Thermal mass
    The ability of a material to absorb, store and release heat. The walls of a building can store heat (or cold) to help the interior temperature change much more slowly than the exterior ambient temperature without additional energy inputs, such as active heating or air conditioning. It is therefore a key component of energy efficient building design and thermal energy storage systems.
    Thermal storage
    See thermal energy storage.
    Thermonuclear fusion
    The process of atomic nuclei combining or fusing using high temperatures to drive them close enough together for this to become possible. Controlled thermonuclear fusion is the principle underpinning nuclear fusion energy.
    Thorium reactor
    A type of nuclear fission reactor that irradiates thorium to produce uranium fuel inside the reactor and sustains a chain reaction to generate heat. Though not free from proliferation risks, thorium reactors produce less nuclear waste and are less weaponisable than those using uranium fuel cycles. China announced the completion of its first experimental thorium reactor in mid-2021.
    Tight gas
    Natural gas produced from reservoirs with such low permeability that the gas is sealed tightly in impermeable, hard rocks and hydraulic fracturing is necessary for a well to produce gas at competitive costs.
    Tight oil
    A type of unconventional oil produced from shales or other very low permeability formations, using hydraulic fracturing and, usually, horizontal drilling. Sometimes referred to as light tight oil. Tight oil is a preferred term to shale oil, which is the term used for the unrelated oil obtained from oil shale. In IEA analysis and statistics, tight oil includes tight crude oil and condensate production except for the United States, for which tight crude oil only is included (US tight condensate volumes are included in natural gas liquids). In the World Energy Outlook, tight oil includes tight crude oil and condensate production except for the United States, which includes tight crude oil only (US tight condensate volumes are included in natural gas liquids.
    Tokamak
    A machine that confines a plasma using magnetic fields in a donut shape that scientists call a torus. It is a leading concept for the confinement of plasma at sufficient density and for sufficient time to sustain nuclear fusion reactions for power plants. One set of magnetic coils generates an intense “toroidal” field, directed the long way around the torus. A central solenoid (a magnet that carries electric current) creates a second magnetic field directed along the “poloidal” direction, the short way around the torus. The two field components result in a twisted magnetic field that confines the particles in the plasma. A third set of field coils generates an outer poloidal field that shapes and positions the plasma. The first tokamak began operation in Russia in 1958. The ITER project is building a large tokamak to explore the physics of burning plasmas.
    Tonne kilometre (tkm)
    An indicator of demand for freight travel, measured as the number of kilometres travelled per tonne of cargo carried over a fixed period such as a year. Used in the calculation of energy efficiency indicators and to project future travel demand. See also passenger kilometre.
    Tonne miles
    See tonne kilometre.
    Tonne of carbon dioxide (t CO2)
    A unit of CO2 measuring 1 tonne.
    Tonne of coal equivalent (tce)
    A unit of energy equal to the energy contained in the one tonne of a standard hard coal. One tce is equivalent to 29.31 GJ on an lower heating value basis.
    Tonne of heavy metal (tHM)
    A means of expressing the quantity of fuel input to nuclear fission or the quantity of nuclear waste, based on the mass of uranium, plutonium, thorium or mixtures of these elements. Not a standardised unit of energy. One tonne of heavy metal waste is less radioactive than one tonne of heavy metal fuel, unless an attempt has been made to calculate equivalence.
    Tonne of oil equivalent (toe)
    A unit of energy equal to the energy contained in the one tonne of a standard crude oil. One toe is equivalent to 41.87 GJ on an lower heating value basis.
    Topping refinery
    The least sophisticated oil refineries, containing only the atmospheric distillation column and possibly a vacuum distillation column. Will obtain those light products that are most easily separated from the crude oil, namely liquefied petroleum gas, naphtha, jet kerosene and gasoil, with a high yield of residual fuel oil.
    Total acid number
    A measure of how corrosive crude oil is. More robust metallurgy is needed to handle a crude with a high TAN number. The TAN scale varies between 0.01 milligrammes KOH (potassium hydroxide) per gramme to 3 mg KOH/g. See also API gravity, sweet crude and sour crude.
    Total energy supply
    Represents domestic demand only, and is equivalent to electricity and heat generation plus the other energy sector, excluding electricity, heat and hydrogen, plus total final consumption, excluding electricity, heat and hydrogen. TES does not include ambient heat from heat pumps or electricity trade. In energy statistics, total energy supply (TES) is made up of production + imports - exports - international marine bunkers - international aviation bunkers ± stock changes. Note, exports, bunkers and stock changes incorporate the algebraic sign directly in the number.
    Total energy supply (WEO)
    Represents domestic demand only, and is equivalent to electricity and heat generation plus the other energy sector, excluding electricity, heat and hydrogen, plus total final consumption, excluding electricity, heat and hydrogen. TES does not include ambient heat from heat pumps or electricity trade.
    Total final consumption
    Is the sum of consumption by the various end-use sectors. TFC is broken down into energy demand in the following sectors: industry (including manufacturing, mining, chemicals production, blast furnaces and coke ovens); transport; buildings (including residential and services); and other (including agriculture and other non-energy use). It excludes international marine and aviation bunkers, except at world level where it is included in the transport sector.
    Total final energy consumption
    While not used in official energy statistics or IEA analysis, TFEC is a variable developed for tracking progress towards target 7.2 of the United Nations Sustainable Development Goals (SDGs). It incorporates total final consumption by end-use sectors, but excludes non-energy use. It excludes international marine and aviation bunkers, except at world level. Typically this is used in the context of calculating the renewable energy share in total final energy consumption (indicator SDG 7.2.1), where TFEC is the denominator. See also total final consumption.
    Total primary energy demand
    See total energy supply. TPED is no longer in use in IEA analysis and statistics.
    Total primary energy supply
    See total energy supply. TPES is no longer in use in IEA analysis and statistics.
    Trading volume
    In oil trade, this is the total number of transactions of a particular contract traded on the futures market during a specified period of time (rather than the underlying volume of oil they represent).
    Traditional use of bioenergy
    See traditional use of biomass.
    Traditional use of biomass
    Refers to the use of solid biomass with basic technologies, such as a three-stone fire or basic improved cook stoves (ISO tier 0-2), often with no or poorly operating chimneys. Forms of biomass used include wood, wood waste, charcoal, agricultural residues and other bio-sourced fuels such as animal dung.
    Transesterification
    A chemical process that converts triglycerides in oils.
    Transhipment
    In oil trade, this is a process whereby a cargo is transferred to a different ship to continue its journey.
    Transmission and distribution (T&D)
    Refers to the high- and low-voltage cable networks for transporting electricity and the high- and low-pressure pipeline networks for transporting gaseous fuels. Includes equipment connected to these networks (so-called in-front-of-the-meter devices) to improve performance, such as energy storage or smart controls. See also distribution system and transmission system.
    Transmission system
    In energy supply via fixed network infrastructure, the transmission system connects large suppliers of energy, such as power plants or liquefied natural gas terminals. In gas supply, the transmission network is at a higher pressure (up to 70 bar or 7 MPa) than the distribution network (up to 2 bar or 200 kPa). In electricity supply, the transmission network is at a higher voltage (up to 1 000 kV or more) than the distribution network (up to 50 kV). See also distribution system.
    Transmission system operator
    An entity responsible for transporting and managing energy from large suppliers to the point where it is passed to the distribution system. TSOs and distribution system operators (DSOs) are generally either state-owned or granted a licence as a network monopoly for a fixed period under a regulatory contract to provide a service and be remunerated by fees claimed via energy bills. See also distribution system operator.
    Transport
    In energy statistics, this represents the transport component of total final consumption. Includes fuels and electricity used in the transport of goods or persons within the territory irrespective of the economic sector within which the activity occurs. Includes fuel and electricity for use in road vehicles or rail vehicles; fuel delivered to vessels for domestic navigation; fuel delivered to aircraft for domestic aviation; and energy consumed in the delivery of fuels through pipelines. All energy consumption from international marine and aviation bunkers is included in transport total final consumption at the world level and not in regional breakdowns.
    Treating
    Oil refining processes whereby intermediate products obtained by distillation and conversion are refined by physical or chemical means to remove substances that impair their odour, colour, stability or performance.

  • U

    Ultra large crude carrier
    Very large crude carriers of 320 000 deadweight tons or greater are also referred to as ULCCs.
    Ultra-high voltage
    Electricity networks operating at greater than 800 kV for either alternating current or direct current power. At higher voltages (and lower currents) losses are reduced, making UHV attractive for long-distance transmission systems. See also high-voltage direct current.
    Ultra-low sulphur diesel
    Diesel fuel with a low sulphur content. Definitions vary according to local standards. In the United States sulphur content must be below 15 ppm, while in Europe the threshold is 50 ppm.
    Ultra-low sulphur fuel oil
    A liquid hydrocarbon fuel with a sulphur content of 0.1% or less by mass.
    Ultra-supercritical (USC)
    A designation for fuel combustion facilities that operate at up to 760 °C and pressure levels of 34 MPa, especially coal-fired power plants. More energy efficient than subcritical or supercritical plants, but also more costly. As of 2023, they can reach 47.5% lower heating value efficiency. See also subcritical and supercritical.
    Unabated coal
    See unabated fossil fuels.
    Unabated fossil fuels
    Fossil fuels used for energy purposes without carbon capture, utilisation and storage (CCUS). In IEA analysis, total fossil fuel use is equal to unabated fossil fuels plus fossil fuels with CCUS plus non-energy use of fossil fuels.
    Unabated gas
    See unabated fossil fuels.
    Unconventional gas
    Gaseous fuels trapped deep underground by impermeable rocks, such as coal, sandstone and shale. Includes shale gas, coal bed methane and tight gas. While different techniques are applied, depending on the type of gas being extracted, one common method is known as hydraulic fracturing. Another key technology is horizontal drilling. See also conventional gas.
    Unconventional oil
    Includes mining and in-situ extra-heavy oil and bitumen (synthetic crudes made by upgrading bituminous, e.g., oil sands in Canada, or extra heavy crude oils, light tight oil, kerogen oil, coal-to-liquids (CTL) and gas-to-liquids (GTL) products, additives and natural gas liquids from unconventional natural gas fields.
    Underground coal gasification (UCG)
    A technique for the gasification of an underground coal resource in situ and retrieval of the resulting synthesis gas at the surface without mining. Its attraction is its potential application to coal resources that are otherwise unprofitable or technically complicated to extract by traditional mining methods. As of 2023, no project has operated past the demonstration stage worldwide.
    Underground thermal energy storage
    A type of energy storage in which an energy-carrying medium is injected below the earth's surface in a way that the energy can be extracted at a future date. It takes advantage of the lower heat losses experienced underground. Most commonly used for relatively long-duration storage, including inter-seasonal storage. A typical set-up might include placing pipes in rocks, soil, sand or clay in the shallow subsurface and pumping a heat transfer fluid into them such that the surrounding material heats up. Other methods include the use of underground caverns or pits to store hot or cold water. Can complement district heating systems well and can also be operated in conjunction with geothermal energy systems to raise the amount of heat available from the system at a later time. The Drake Landing Solar Community borehole seasonal storage system in Canada has been in operation since 2007 with GWh-scale storage capacity.
    Undiscovered
    Where the suitability for CO2 storage has not been determined for a specific subsurface storage formation, storage resources are classified as undiscovered.
    UNGG reactor
    A Uranium Naturel Graphite Gaz nuclear fission reactor, a type developed in France in the 1950s. Along with Magnox and advanced gas-cooled reactors, it was the main form of gas-cooled reactor and ten units were built (nine in France, one in Spain) between 1956 and 1972. It was graphite moderated, cooled with carbon dioxide and fuelled with natural uranium metal. The last UNGG reactor ceased operation in 1994.
    Unleaded motor gasoline
    Motor gasoline where lead compounds have not been added to enhance octane rating. May contain traces of organic lead.
    Upstream
    In energy supply, the stage of the supply chain that extracts, gathers and processes primary energy resources. In the oil and gas industry, it includes exploration, appraisal, development and production activities pertaining to reserves of crude oil, natural gas liquids and condensates. Upstream (exploration and extraction) connects to midstream (shipping and transport of crude oil or other unrefined energy products), which connects to downstream (refining, shipping and marketing). See also downstream and midstream.
    Useful energy
    Energy available to end users to satisfy their need for energy services. As a result of transformation losses at the point of use, the amount of useful energy is lower than the corresponding final energy demand for most technologies. See also energy services.
    Utilisation rate
    A measure of the capacity factor of an oil refinery's distillation units. Calculated by dividing the gross input to these units by the operating capacity of the units.
    Utility
    In energy analysis, utility typically refers to an entity that maintains the infrastructure for a public service (often also providing a service using that infrastructure). Network services, such as the provision of electricity or gaseous fuels, are often natural monopoly businesses and public utilities are therefore subject to forms of public control and regulation. The extent to which companies active in electricity generation, electricity retail and gas retail are regulated as public utilities depends of the extent to which these markets have been unbundled into separate markets for generation, transmission, distribution and retail.

  • V

    Vacuum distillation
    A method of distillation under reduced pressure (less than atmospheric), which lowers the boiling temperature of the liquid being distilled. This technique permits the production of distillates at a lower temperature than would be necessary in atmospheric distillation, thus avoiding coke formation. Used in oil refining.
    Vacuum residue
    A heavier liquid residue from the distillation of atmospheric residue under vacuum. See also atmospheric residue and cracked residue.
    Valley of death
    A concept in innovation theory that describes a period in which a new technology or product requires a significant increase in risk capital to demonstrate its effectiveness, affordability and marketability. This period often results from a mismatch in available capital from public and private sources: available R&D funding is no longer appropriate and private investors generally do not have the risk appetite to support this increase in both capital requirements and risk.
    Value-adjusted levelised cost of electricity
    A more complete metric to evaluate the competitiveness of power generation technologies, which includes all direct technology costs (LCOE) combined with the estimated value of three services provided to the system: energy, flexibility and capacity.
    Vapour compression
    A means of converting electrical or mechanical energy to a source of cooling or heating. A vapour-compression refrigeration system contains a compressor, condensor, a thermal expansion (or throttle) valve and an evaporator. For cooling, a vapour-phase refrigerant is compressed to a higher pressure, raising its temperature before it passes through the condensor, where heat is transferred to an external medium (such as the air). In the condensor, the refrigerant becomes liquid and is cooled, before the pressure is abruptly reduced by flash evaporation in the expansion valve to reduce the temperature further. The final stage is the cooling of the target (for example, indoor air) by moving air across the coils or tubes of an evaporator while the cold refrigerant passed through them and becomes fully regasified. A heat pump runs the same cycle in the opposite direction.
    Vapour recovery unit
    A small compressor designed to capture emissions that build up in pieces of equipment across the oil and natural gas supply chains. For instance, it can capture gases that accumulate in oil storage tanks and which are otherwise periodically vented to the atmosphere to prevent explosion.
    Variable renewable energy
    Sources of renewable energy (usually electricity) where the maximum output of an installation at a given time depends on the availability of fluctuating environmental inputs. VRE includes a broad array of technologies such as wind power, solar PV, run-of-river hydro, concentrating solar power (where no thermal storage is included) and marine (tidal and wave).
    Vented methane emissions
    Methane emissions from methane venting.
    Venting
    See methane venting and CO2 venting.
    Very large crude carrier
    Oil tanker with a capacity of 200 000 deadweight tons or more. Carries mainly crude oil, but also fuel oil exports, in parcel sizes of 240 000 deadweight tons (around two million barrels) or greater. Being the largest vessels in the fleet, VLCCs have limited access to many ports and shipping lanes due to draft restrictions. Typical routes include Middle Eastern crude exports to Europe, the United States and the Far East. VLCCs of 320 000 deadweight tons or greater are also referred to as ultra-large crude carriers. See also Aframax, Panamax, Handymax, Handy vessel and Suezmax.
    Very-low sulphur fuel oil
    A liquid hydrocarbon fuel with a sulphur content of 0.1-0.5% by mass.
    Visbreaking
    A thermal cracking process in oil refining whereby heavy atmospheric or vacuum-distillation bottoms are cracked at moderate temperatures to make light products and to produce a lower viscosity residue than the initial feed to the unit.
    Viscosity
    The measure of a fluid’s internal resistance to flow. This is not typically a problem for light products and is usually applicable to residual fuel oils that are derived from atmospheric and vacuum residues. These need to be maintained at temperatures of around 65-70 °C to ensure that they are sufficiently fluid to be usable, otherwise they become a semi-solid tar. Diesel and gasoil are usually sufficiently fluid so that viscosity is not an issue, although at temperatures below 0 °C diesel and gasoil can become cloudy and viscous, preventing their use in engines or boilers. The addition of kerosene (with a freezing point of around -50 °C) significantly improves the cold weather properties of gasoil and diesel.
    Volatile organic compounds
    Compounds with high vapour pressure and low water solubility. Many are human-made chemical solvents that are used and produced in the manufacture of paints, pharmaceuticals and refrigerants. Methyl tert-butyl ether (MTBE), a fuel additive is an example of a VOC and VOCs are often components of petroleum fuels and hydraulic fluids, such as those for hydraulic fracturing. VOCs are common ground-water contaminants. They have short- and long-term adverse health effects.
    Volume-to-mass ratio
    In energy statistics, this ratio is used to indicate oil demand by product. It is calculated as barrels of oil products divided by the mass of the oil products (in boe/tonne) and is the inverse of density.

  • W

    Watt (W)
    The unit of power (or radiant flux) in the International System of Units. Technically, one watt is the rate at which electrical work is performed when a current of one ampere (A) flows across an electrical potential difference of one volt (V). It is most commonly used to denote the capacity of an electrical generator or an electrical load. For example, if a power plant with an electrical capacity (after self-consumption) of 100 watts generates for one hour it will produce 100 watt hours. See also watt hour.
    Watt hour
    A unit of energy equal to one watt of power for one hour. It is most frequently used in the electricity sector for electrical energy, and sometimes for heat, but can in practice be applied to any form of energy. It is equivalent to 3.6 kJ.
    West Texas Intermediate
    A pricing benchmark for oil based on the WTI Crude Oil futures contract traded on the New York Mercantile Exchange (NYMEX). WTI is a grade or mix of crude oil also known as Texas light sweet. Oil from any location can be considered WTI if the oil meets the criteria for this grade. The term is sometimes used to refer to spot prices, assessed prices or other futures prices for that oil. While definitions vary slightly, WTI's lightness is between 37° and 42° API gravity and its sweetness is below 0.42% sulphur content. See also sweet crude and light crude.
    White certificates
    See energy efficiency.
    White spirit
    Industrial spirit with a flash point above 30 °C. The distillation range of white spirit is 135-20 °C. Mainly for non-energy uses.
    White spirit and industrial spirit
    Includes white spirit and industrial spirit
    White spirit and special boiling point industrial spirits
    Includes white spirit and industrial spirit
    Wildcat well
    An oil or gas well drilled in an unproved area. See also proved.
    Wind energy
    The kinetic energy of the wind exploited for electricity generation in wind turbines. Includes onshore wind and offshore wind. Does not usually include wind energy harvested for mechanical force for water pumps, grinding or other applications.
    Workover
    An operation on a producing oil or gas well to restore or increase production. Tubing may be pulled out and the casing at the bottom of the well pumped or washed free of accumulated sand. Well bores may be fractured or redrilled, gravel packing may be used, or pumps may be replaced.
    Worldscale
    The standard system for assessing freight rates for oil tankers. Once a year, a set of base voyage costs (including bunkers, port costs, etc. for both laden and return ballast legs) is published for a theoretical standard vessel plying its trade between each of the world’s main loading and discharging ports. Spot freight rates are commonly expressed as percentages of those theoretical rates. For example, if very large crude carrier rates are said to be WS67, actual rates are two-thirds of the base or flat rates published at the beginning of the year.
    Worldwide Harmonised Light Vehicles Test Procedure
    A global standard for determining the levels of pollutants, CO2 emissions and fuel economy of road vehicles, including electric vehicles. The Global Technical Regulations were published in 2015 and have been integrated into regulations around the world. The IEA uses WLTP in its assessments of vehicle fuel economy.

  • Z

    Zero carbon-ready buildings
    A zero carbon-ready building is highly energy efficient and either uses renewable energy directly or an energy supply that can be fully decarbonised, such as electricity or district heat.
    Zero emissions vehicles
    Vehicles that operate without tailpipe CO2 emissions (battery electric, plug-in hybrids and fuel cell vehicles).