Reference

Sustainability terms and definitions

Carbon accounting and sustainability terms: how emissions are measured, allocated and regulated, from lifecycle assessment to land use, feedstocks, fuels and hydrogen. These are general reference definitions, not tied to any one report.

189 terms · Updated 29 Sep 2026

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45ZCF-GREET: The version of the GREET model published by the U.S. Department of Energy and Treasury specifically to calculate carbon intensities for the Section 45Z credit.

A

Accounting credit: A deduction from a product's reported emissions that comes from a rule or a claimed benefit rather than from a physical cut in the supply chain. Examples include credits for co-products, soil-carbon gains or avoided waste.
Additionality: The test of whether a claimed benefit would have happened anyway. A feedstock, credit or project is additional only if the fuel demand actually caused it.
Allocation (co-product allocation): Splitting the emissions of a shared process among the products that come out of it. Crushing soybeans yields both oil and meal, so the farm's emissions must be divided between them. The splitting rule can move a result by more than 10 g CO₂e/MJ.
Allocation hierarchy: The order of preference ISO 14044 sets for handling co-products: first avoid allocation by subdividing processes or expanding the system, then allocate by physical relationships, and only then by economic value. No regulatory framework follows this hierarchy strictly.
Ammonia: grey, blue and green: Ammonia (NH₃) is the base of nearly all synthetic nitrogen fertilizer, made by combining hydrogen with nitrogen from the air in the Haber-Bosch process. The color follows the hydrogen: grey ammonia uses hydrogen from unabated natural gas; blue ammonia captures and stores the CO₂ from that step; green ammonia uses hydrogen from electrolysis on renewable power.
Amortization period: The number of years over which a one-off land-use emission is spread when it is converted into a per-megajoule figure. A longer period makes the same emission look smaller per year. GLOBIOM's palm value is 231 g CO₂e/MJ over 20 years, 185 g over CORSIA's 25 years and about 154 g over 30 years.
Animal by-product categories 1, 2 and 3: The EU's risk classes for animal material not intended for human consumption, set by Regulation (EC) No 1069/2009. Category 1 is the highest risk, such as material linked to transmissible spongiform encephalopathies; Category 2 includes fallen stock and manure; Category 3 is low-risk material from healthy animals. Categories 1 and 2 are barred from feed and mostly burned for energy, so using them displaces little; Category 3 fats compete in feed, pet food and oleochemicals, and palm is their likely substitute.
Annex IX Part B: The list in the EU RED of feedstocks, principally used cooking oil and animal fats, whose contribution to transport targets is capped because supply is limited. The cap is 1.7 percent of transport energy; Germany has raised it to 1.9 percent.
Annex V and Annex VIII: Annex V of the EU RED sets the calculation rules, the 94 g fossil comparator and the typical and default values for biofuels. Annex VIII sets provisional ILUC estimates, 55 g CO₂e/MJ for oil crops, which are reported but not counted toward compliance.
Anti-dumping investigation: A trade inquiry into whether imports are sold below fair value, which can end in extra import duties.
AR6: The Intergovernmental Panel on Climate Change's Sixth Assessment Report, completed in 2021 to 2023. It updated the warming factors used to convert methane and nitrous oxide into CO₂e: 27 for biogenic methane and 273 for N₂O over 100 years. The EU RED still uses the older values of 25 and 298.
Argonne National Laboratory: A U.S. Department of Energy research laboratory near Chicago that develops and maintains the GREET and CCLUB models.
Attributional accounting (attributional LCA): A way of measuring emissions that divides up the pollution of an existing supply chain among its products, as a snapshot. It asks: what share of today's emissions belongs to this fuel? It ignores the knock-on effects of extra demand. The EU RED, CORSIA core values and GREET direct results are attributional, and they assign wastes zero upstream burden.
Avoided-emissions credit: A credit claimed because using a material prevents emissions that would otherwise occur, for example waste oil that would have rotted and released methane.

B

Biogenic carbon: Carbon that a plant recently pulled out of the air through photosynthesis, as opposed to fossil carbon locked underground for millions of years. Most frameworks treat biogenic CO₂ released on combustion as neutral, because the next crop reabsorbs it.
Biomass-based diesel: The U.S. regulatory category covering both FAME biodiesel and renewable diesel (HVO).
Blue hydrogen: Hydrogen made from natural gas with the CO₂ captured and stored. Its real footprint depends on how much CO₂ is actually captured and how much methane leaks upstream. At 93 percent capture and 0.2 percent leakage it cuts emissions about 75 percent versus grey; operating plants such as Quest and Port Arthur capture only 50 to 60 percent.
Buffer pool: A reserve of credits that a carbon program sets aside and does not sell, used to cover losses if stored carbon is later released. It works like an insurance fund for reversals.

C

CA-GREET: The California Air Resources Board's adaptation of GREET, used to certify fuel pathway carbon intensities under the LCFS.
Capture rate: The share of a plant's CO₂ actually captured. The nameplate rate is what a plant is designed for; the realized rate is what it achieves, and it is often lower. Retrofits typically capture only the concentrated process stream, not the flue gas from burners.
CARB (California Air Resources Board): California's air-quality and climate regulator, which runs the LCFS and sets its ILUC values using GTAP-BIO.
Carbon accounting: The practice of measuring, allocating and reporting the greenhouse gases linked to a product, company or activity, using defined rules for what counts, where the boundary sits and which baseline applies. Different rulebooks give different answers for the same physical fuel.
Carbon capture and storage (CCS): Separating CO₂ from an industrial stream and injecting it into deep geological formations for permanent storage. Captured fossil CO₂ lowers emissions but does not remove carbon from the atmosphere.
Carbon debt: The one-off pulse of carbon released when land is cleared or converted for a fuel crop, from burned or decaying vegetation and disturbed soil. The fuel must then save emissions for years before it has repaid that debt. Converting Southeast Asian peat rainforest to palm releases about 3,452 t CO₂ per hectare, by one widely cited estimate.
Carbon intensity (CI): The lifecycle emissions per unit of fuel energy, usually in grams of CO₂e per megajoule. It is the number that incentive programs such as the LCFS and Section 45Z pay on: the lower the CI, the larger the credit.
Carbon neutral (carbon neutrality): A claim that a product's net lifecycle emissions equal zero. It is a much stronger claim than being lower-carbon than the alternative.
Carbon removal (durable removal): Taking CO₂ out of the atmosphere and storing it for a long time, typically centuries, in geological formations, mineral form or stable materials. Carbon held in short-lived products, such as fuel, does not count.
Carbon-debt payback time: The years needed for a biofuel's annual savings to repay the carbon debt from land conversion. It equals the allocated debt divided by the yearly saving per hectare.
Carbon-intensity-priced offtake: An offtake whose price rises or falls with the verified carbon intensity of the fuel delivered, rewarding the producer for decarbonizing inputs such as hydrogen.
CCLUB (Carbon Calculator for Land Use and Land Management Change from Biofuels Production): Argonne's module that attaches land-use emissions to GREET results. It applies 38.1 t CO₂e per hectare per year for peat oxidation and gives about 7.9 g CO₂e/MJ of ILUC for soybean biodiesel.
Central estimate: The single most representative value within a range of plausible results, used as the headline figure. The range around it shows how much the answer depends on assumptions.
Cerrado: The vast tropical savanna of central Brazil, rich in below-ground carbon and a major frontier of soybean expansion.
Certification scheme (voluntary scheme): A private program recognized by the European Commission to audit and certify that biofuel feedstocks meet sustainability and waste-status rules. ISCC is the largest. Critics point to weak audits at the point where waste status is attested.
Cerulogy: A UK consultancy specializing in the sustainability of alternative fuels, whose analyses on waste and residue supply are cited by NGOs and regulators.
Chain of custody: The documented trail that follows a material from origin to final product, showing who held it and what claims travel with it. Mass balance is the most common chain-of-custody model for biofuels.
Co-processing: Feeding a share of vegetable oil or waste fat into an existing petroleum refinery unit alongside crude-derived feed, rather than building a dedicated plant. The renewable share of the output is tracked by accounting rules.
Co-product: A useful output produced alongside the main product, such as soybean meal from crushing, glycerol from biodiesel, or propane and naphtha from HVO. Co-products share the upstream emissions through allocation or earn credits through system expansion.
CO₂e (carbon dioxide equivalent): A common unit that expresses different greenhouse gases as the amount of CO₂ that would cause the same warming. One gram of N₂O counts as 273 to 298 g CO₂e depending on the factor set used.
Cold-flow properties: How well a fuel keeps flowing in cold weather without forming wax crystals that clog filters. Measured by cloud point and cold filter plugging point, they are the main reason HVO is isomerized.
Consequential accounting (consequential LCA): A way of measuring emissions that asks what changes in the world because of an extra unit of demand. It captures ripple effects such as new land clearing or former users of a waste switching to another material.
Converted refinery and standalone plant: A converted refinery is a former petroleum refinery rebuilt to process lipids into HVO, often keeping its gas-fired hydrogen reformer; a standalone plant is built new for the purpose. Examples of conversions include Phillips 66 (NYSE:PSX) at Rodeo and Eni (BIT:ENI) at Venice and Gela.
Core lifecycle value: CORSIA's term for the direct, attributional part of a fuel's lifecycle emissions, excluding ILUC. The ILUC value is added separately.
CORSIA (Carbon Offsetting and Reduction Scheme for International Aviation): The International Civil Aviation Organization's global scheme, adopted in 2016, under which airlines offset growth in international aviation emissions or cut them with eligible lower-carbon fuels. Its lifecycle values combine a core value with an ILUC value, amortized over 25 years against an 89 g CO₂e/MJ jet-fuel baseline.
CORSIA eligible fuel: A sustainable or lower-carbon aviation fuel that meets CORSIA's sustainability criteria, including at least 10 percent lower lifecycle emissions than the 89 g baseline, which puts the threshold near 80 g.
Counterfactual: What would have happened without the activity being assessed. A waste's counterfactual is its fate if the fuel plant did not take it, for example animal feed, soap or disposal.
Cover crop: A crop grown mainly to protect or improve soil between cash crops, rather than for sale. Some oilseed cover crops can also yield fuel feedstock. Several U.S. states assign cover-crop oils zero ILUC.
Cradle-to-grave: A lifecycle boundary that runs from raw material extraction or cultivation through processing and use to final disposal or combustion. For fuels the equivalent term is well-to-wheel.
Crop oil (crop-oil HVO): Vegetable oil pressed from crops grown for the purpose, such as rapeseed, canola, soybean, sunflower and palm, as opposed to wastes and residues. Crop-oil pathways carry fertilizer, soil N₂O and land-use burdens that waste pathways avoid.
Crude tall oil: A by-product of the kraft pulping process that turns pine wood into paper pulp. It has an established market in pine chemicals, so diverting it to fuel carries displacement risk.
Crushing: Breaking oilseeds to separate oil from the solid meal. It can be done by mechanical pressing, by solvent extraction with hexane, or both in sequence; solvent extraction recovers more oil.
Cut-off: A decision to leave small or hard-to-measure inputs out of an assessment. ISO 14044 permits cut-offs when they are documented.

D

DAYCENT and DNDC: Process-based models that simulate soil carbon and nitrogen cycles day by day to estimate site-specific N₂O emissions. DAYCENT is the daily version of the CENTURY model; DNDC stands for DeNitrification-DeComposition.
Decarboxylation and decarbonylation: Reaction routes that strip oxygen from fats by removing it as CO₂ (decarboxylation) or CO (decarbonylation). They use less hydrogen than hydrodeoxygenation but lose one carbon atom per chain, lowering yield.
Default value, typical value and actual value: Three ways a regulator can assign a fuel's emissions. A typical value is a representative estimate; a default value is a deliberately conservative version of it that producers may use without their own data; an actual value is calculated from a producer's own verified data.
Diesel benchmark: The declining carbon-intensity target that diesel substitutes are measured against under California's LCFS. Crop-oil volumes above the program's 20 percent cap are assigned the benchmark intensity and earn no credit.
Direct emissions: Emissions that come from the supply chain's own physical steps, such as farming, fertilizer, processing, hydrogen and transport. They exclude market-driven effects such as indirect land-use change.
Direct land-use change (dLUC): Emissions from converting a specific plot to grow the feedstock, such as clearing forest for a plantation. It is traceable to the supply chain, unlike indirect land-use change.
Directive (EU) 2018/2001 (RED II): The recast Renewable Energy Directive that set EU renewable energy rules for 2021 to 2030, including the lifecycle calculation method in Annex V.
Directive (EU) 2023/2413 (RED III): The 2023 amendment to RED II. It raised the EU's binding 2030 renewable energy target to 42.5 percent and set transport goals of either a 14.5 percent cut in greenhouse-gas intensity or a 29 percent renewable share. It keeps RED II's 94 g comparator, energy allocation and the Annex V values, and caps food and feed crop biofuels.
Displacement (residue displacement): What happens when a fuel plant takes a waste or residue that someone else was already using: the former user must buy a replacement, often palm or soybean oil, and that replacement carries emissions. Consequential accounting counts this; attributional accounting does not.
Distillers corn oil: Oil recovered from the leftovers of corn-ethanol production. It carries none of the ethanol plant's emissions under attributional rules, but it already has a market in animal feed.
Double-cropping and relay-cropping: Growing two crops on the same field in one year. In double-cropping the second is planted after the first is harvested; in relay-cropping it is sown into the standing first crop. Both let an oilseed use land that would otherwise sit fallow.
Drop-in fuel: A renewable fuel chemically similar enough to its fossil counterpart that it can be used in existing engines, tanks and pipelines without modification, and neat (100 percent) rather than blended.

E

Economic allocation: Splitting shared emissions in proportion to the market value of each co-product. For soybean it lands close to energy allocation, but it shifts whenever relative prices move.
Electrolysis (electrolytic hydrogen): Splitting water into hydrogen and oxygen with electricity, using about 55 kWh per kilogram of hydrogen. Its footprint is set by the power source.
Embodied emissions: Emissions released in making equipment and infrastructure, such as tractors, refineries and pipelines, spread over their useful life.
Emission factor: A conversion rate that turns an activity into emissions, for example the share of applied nitrogen fertilizer that escapes as N₂O. The IPCC's 2019 update set 1.6 percent for synthetic nitrogen in wet climates and 0.5 percent in dry ones, replacing a single 1 percent.
Emissions (greenhouse gas emissions): Releases of heat-trapping gases, chiefly carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O). In lifecycle accounting they are converted into a single CO₂-equivalent figure.
Energy allocation (energy-allocated basis): Splitting shared emissions in proportion to the energy content of each co-product. It is the EU RED's rule. Soybean oil is about 19 percent of crushed mass but about a third of its energy, so energy allocation assigns the oil about 1.8 times the burden of mass allocation.
Enhanced-efficiency nitrogen fertilizer: Fertilizer formulated to release nitrogen slowly or to block the microbial steps that produce N₂O, using coatings or chemical inhibitors. It is a mitigation for soil nitrous oxide.
EPA (U.S. Environmental Protection Agency): The federal agency that runs the Renewable Fuel Standard and its lifecycle analysis, including ILUC.
Exothermic reaction: A chemical reaction that releases heat. Hydrotreating is strongly exothermic, and plants recover that heat to cut their energy use.

F

FAME (fatty acid methyl ester, biodiesel): First-generation biodiesel made by reacting fats with methanol. It keeps oxygen in the molecule, which limits its blend share: the European diesel standard EN 590 caps it at 7 percent. It is chemically distinct from HVO.
Food and feed crop cap: The RED limit on biofuels from food and feed crops: the lower of 7 percent of transport energy or each member state's 2020 share plus 1 percentage point.
Foregone sequestration: The carbon that land would have absorbed if it had been left to regrow naturally instead of being farmed for fuel. No regulatory framework charges for it, although CORSIA treats it as a sensitivity case.
Fossil diesel (petroleum diesel): Diesel refined from crude oil. In lifecycle accounting it is the reference fuel that HVO displaces, represented by a single comparator value.
Fossil fuel comparator (fossil baseline): The fixed emissions value for the fossil fuel being replaced, against which savings are measured. The EU RED uses 94 g CO₂e/MJ for transport fuels; the 2009 RED used 83.8 g, CORSIA uses 89 g for jet fuel, and the RED uses 183 g per megajoule of electricity for power generation.
Free fatty acids (FFA): Fatty-acid chains that have broken free of their glycerol backbone, common in degraded oils such as used cooking oil and PFAD. High FFA content makes FAME production harder but suits hydroprocessing.
Fuel pathway: A specific combination of feedstock, origin, process and energy inputs that regulators certify with its own carbon intensity, for example "U.S. soybean oil to renewable diesel with grid power and grey hydrogen."

G

g CO₂e/kWh: Grams of CO₂-equivalent per kilowatt-hour of electricity generated. It is the natural unit for backup generators and power plants.
g CO₂e/MJ: Grams of CO₂-equivalent emitted per megajoule of fuel energy. It is the standard unit for comparing fuels because it normalizes for energy content rather than volume or weight.
GHG quota (Germany): Germany's greenhouse-gas reduction quota for fuel suppliers, which requires a set percentage cut in the emissions of fuel sold. Germany has not counted palm-based fuels toward it since 2023.
GHG saving (percentage saving): The reduction a fuel achieves against the fossil comparator: comparator minus pathway intensity, divided by the comparator. At 94 g, a fuel of 14 g saves 85 percent.
Global warming potential (GWP): A factor that expresses how much heat a gas traps over a set period relative to CO₂. GWP100 uses a 100-year window and is the regulatory norm; GWP20 uses 20 years and weights short-lived methane much more heavily.
GLOBIOM (Global Biosphere Management Model): An economic model of global agriculture, forestry and bioenergy land use developed by IIASA in Austria. It tends to produce high ILUC values for vegetable oils because it models strong substitution toward palm, including palm expansion onto peat. Its analysis for the European Commission gave 231 g CO₂e/MJ for palm, 150 g for soybean and 65 g for rapeseed over 20 years.
Glycerol (glycerine): The three-carbon backbone released when triglycerides are split. It is a co-product of FAME biodiesel, not of HVO.
Green hydrogen (renewable electrolytic hydrogen): Hydrogen made by electrolysis powered by renewable electricity such as wind or solar. Dedicated wind power gives about 1 kg CO₂e per kg of hydrogen. Hydrogen from nuclear-powered electrolysis is sometimes called pink hydrogen.
GREET (Greenhouse gases, Regulated Emissions, and Energy use in Technologies): Argonne's lifecycle model for fuels and vehicles, the reference tool for U.S. fuel carbon accounting. R&D GREET is the research version; CA-GREET and 45ZCF-GREET are regulatory adaptations.
Grey hydrogen: Hydrogen made from natural gas, usually by steam methane reforming, with the CO₂ vented to the atmosphere. It is the default at most refineries. It emits about 10 to 14 kg CO₂e per kg of hydrogen.
GTAP-BIO: A version of the Global Trade Analysis Project model from Purdue University, extended to represent biofuels and land use. It is a computable general equilibrium model that simulates how the whole world economy adjusts to extra fuel demand. CARB's GTAP-BIO values are 71.4 g CO₂e/MJ for palm, 29.1 g for soybean and 14.5 g for canola, at the low end of published ILUC estimates.

H

HEFA (hydroprocessed esters and fatty acids): The technical name for the hydroprocessing route that turns fats and oils into paraffinic fuels. It produces both HVO for road use and most of today's sustainable aviation fuel.
High ILUC-risk biofuel: An EU category for crop-based fuels whose expansion has significantly moved into high-carbon land, identified in a 2019 delegated regulation that limited the category to palm oil. Their counting toward targets is to be phased out by 2030.
High-oleic soybean oil: Soybean oil bred to contain more monounsaturated fat and fewer double bonds. It needs less hydrogen to process, which lowers HVO emissions by about 1 g CO₂e/MJ.
High-temperature electrolysis: Electrolysis run at several hundred degrees using solid-oxide cells, which needs less electricity per kilogram because part of the energy comes as heat, for example from a neighboring process.
HVO (hydrotreated vegetable oil, renewable diesel): A paraffinic diesel made by reacting vegetable oils, waste oils or animal fats with hydrogen. It is chemically almost identical to the hydrocarbons in fossil diesel, contains no oxygen and can be used neat. In the United States it is usually called renewable diesel.
Hydrodeoxygenation (HDO): The reaction route that removes oxygen from fats as water by adding hydrogen. It keeps every carbon atom, maximizing yield, but consumes the most hydrogen.
Hydroprocessing (hydrotreating): Refining a feedstock by reacting it with hydrogen at high temperature and pressure over a catalyst. For HVO it saturates double bonds and removes oxygen, turning oil into hydrocarbons.
Hydrotreating catalyst: The metal compounds that make hydroprocessing work, typically sulfided nickel-molybdenum (NiMo) or cobalt-molybdenum (CoMo). They are replaced every few years and usually recycled for their metals.
Hygienisation: Heat treatment that sterilizes animal by-products to destroy pathogens and prions before further use. For Category 1 and 2 material the EU standard is pressure sterilization at 133 °C and 3 bar for 20 minutes. The RED's animal-fat values exclude hygienisation emissions.

I

ICAO (International Civil Aviation Organization): The United Nations agency for international civil aviation, based in Montreal. It runs CORSIA and publishes its default lifecycle values.
ICCT (International Council on Clean Transportation): An independent nonprofit research organization that analyzes transport emissions for policymakers.
IEA (International Energy Agency): The Paris-based intergovernmental energy analysis body.
ifeu (Institut für Energie- und Umweltforschung Heidelberg): A German environmental research institute.
Indirect emissions: Emissions caused outside the supply chain by the market reaction to extra demand, such as land cleared elsewhere or substitute materials used by displaced buyers.
Indirect land-use change (ILUC): Land clearing that happens elsewhere because fuel demand diverts crops from food and feed markets, raising prices and pulling new land into production. It cannot be observed directly and is estimated with economic models. Published ILUC values for vegetable oils run from about 7 to more than 230 g CO₂e/MJ, wider than the entire direct footprint.
Induced effects (market-mediated effects): Changes triggered through prices and trade rather than through the supply chain itself. Higher demand for one vegetable oil raises prices, which draws more land into production somewhere else.
Intermediate oilseed (intermediate crop): An oilseed grown in the gap between main crops in an existing rotation, such as winter canola, carinata (Ethiopian mustard), camelina or pennycress. Because it uses otherwise idle land, it is assumed to cause little or no ILUC.
IPCC (Intergovernmental Panel on Climate Change): The UN body that assesses climate science and publishes the default emission factors and warming potentials that carbon accounting relies on.
IRS Notice 2026-53: U.S. Treasury guidance on the amended Section 45Z credit, under which used cooking oil imported from outside the United States, Mexico and Canada is ineligible after 2025.
ISCC (International Sustainability and Carbon Certification): The largest voluntary certification scheme recognized under the EU RED. It attests waste status and sustainability along biofuel supply chains. It has faced criticism over audit weaknesses at the point where waste status is attested.
ISO 14040 and ISO 14044: The International Organization for Standardization's core standards for life cycle assessment. ISO 14040 sets principles and framework; ISO 14044 sets requirements, including the allocation hierarchy. They are method standards, not compliance schemes, and they allow either attributional or consequential framing.
ISO 14067: The ISO standard for calculating the carbon footprint of a product. It requires transparent, separate reporting of biogenic carbon and direct land-use change.
Isomerization (isomerized): Rearranging straight-chain paraffins into branched ones with the same formula, usually over a noble-metal catalyst such as platinum. Branched molecules stay liquid at lower temperatures, improving cold-flow properties.

J

JRC (Joint Research Centre): The European Commission's in-house science service. It builds the typical and default values in the RED from modeled supply chains rather than plant data.

K

kg CO₂e/kg H₂: Kilograms of CO₂-equivalent emitted per kilogram of hydrogen produced, the standard measure of hydrogen's carbon intensity.

L

Land-use change (LUC): Any shift in how land is used or covered, such as forest to cropland, and the carbon it releases or stores. It includes both direct and indirect effects.
LCFS (Low Carbon Fuel Standard): California's program, adopted in 2009, that requires fuel suppliers to cut the average carbon intensity of their fuels each year, with tradeable credits for fuels below the benchmark. Amendments effective 1 July 2025 cap crop-oil credits at 20 percent of each company's volume and bar palm-derived fuels.
Life cycle (lifecycle): All the stages of a product's existence, from raw materials to end of life. A lifecycle emission figure adds up every stage inside the chosen boundary.
Life cycle assessment (LCA): The standardized method, set out in ISO 14040 and 14044, for totaling the environmental impacts of a product across its life cycle. It can be run on an attributional or consequential basis.
Light ends, renewable naphtha and propane: The lighter co-products of HVO production. Light ends are gases and volatile liquids; renewable naphtha is a gasoline-range liquid used in petrochemicals or blending; propane comes from the glycerol backbone and can displace fossil LPG.
Lower heating value (LHV): The energy released when a fuel burns, excluding the heat recoverable by condensing the water vapor produced. Fuel lifecycle figures are normally quoted on an LHV basis.

M

Main-season crop: A crop that occupies a field for its full growing season, displacing whatever else could have been grown there.
Make-up hydrogen: The fresh hydrogen fed to a hydroprocessing unit to replace what the reactions consume and what is lost in purge and dissolved gases. It is higher than the chemical minimum.
Marginal land: Land of low agricultural value, often degraded or unproductive, that is not needed for food. Fuel crops grown there are promoted as avoiding competition with food, though yields are usually lower.
Mass allocation: Splitting shared emissions in proportion to the weight of each co-product. It is GREET's default for soybean, and it favors the oil, which is light relative to the meal.
Mass balance: A chain-of-custody method that allows certified and uncertified material to be physically mixed, provided the quantity sold as certified never exceeds the certified quantity bought. It tracks volumes on paper, which makes it hard to prove what is physically in a tank.
Meal and cake: The protein-rich solids left after oil is extracted from oilseeds. They are sold as animal feed and take a share of upstream emissions as co-products.
Megajoule (MJ): A unit of energy equal to one million joules. A litre of diesel holds about 36 MJ; a kilowatt-hour equals 3.6 MJ.
Methane (CH₄): A greenhouse gas about 27 times as potent as CO₂ over 100 years and over 80 times over 20 years. In this sector it comes chiefly from decaying palm mill effluent and from leaks in natural-gas supply chains.
Methane capture (biogas capture): Covering palm oil mill effluent ponds or treating the effluent in digesters so that methane is collected and burned or used rather than vented.
Methane leakage (upstream methane): Natural gas that escapes during extraction, processing and transport before it reaches the plant. Because methane is a potent greenhouse gas, even a few percent of leakage can erase much of blue hydrogen's benefit. At 8 percent leakage blue hydrogen's reduction versus grey falls from about 75 to about 45 percent.
Mineral soil: Ordinary soil made mostly of weathered rock particles, as opposed to organic peat soil. Palm grown on mineral soil has a far smaller footprint than palm on drained peat.
MIRAGE: A global economic model from the International Food Policy Research Institute, used in the EU's 2011 ILUC study. It is an earlier counterpart to GLOBIOM in the European debate.
Model output: A number produced by simulation rather than measured. All ILUC values are model outputs. That an effect is unobservable is not evidence that it is zero.
Monte Carlo analysis: A technique that runs a model thousands of times with randomly varied inputs to map the range of possible results.

N

Net-negative: A product or activity that removes more greenhouse gas than it emits over its life cycle.
Net-zero: A state in which remaining emissions are exactly balanced by durable removals. It differs from "low-carbon", which only means fewer emissions than an alternative.
Nitrogen fixation: The process by which legumes such as soybean, with help from root bacteria, convert atmospheric nitrogen into plant nutrients, reducing the need for synthetic fertilizer.
Nitrous oxide (N₂O): A greenhouse gas about 273 times as potent as CO₂ over 100 years, released mainly when soil microbes process nitrogen fertilizer. It is the largest and least certain emission term in crop-based fuels.
Nm³ (normal cubic metre): A volume of gas measured at standard conditions of 0 °C and one atmosphere, used to state hydrogen consumption.

O

OBBBA (One Big Beautiful Bill Act): The 2025 U.S. budget law that amended Section 45Z, excluding ILUC for fuel produced after 2025 and restricting feedstocks to North America.
Offset (external offset): A credit bought from a project outside the supply chain, such as forest protection, to cancel emissions on paper. Offsets do not change the product's physical footprint.
Offtake (offtake agreement): A contract in which a buyer commits in advance to purchase a share of a producer's future output, often for several years. Offtakes give lenders confidence to finance a plant.
Oleochemicals: Chemicals made from fats and oils, such as soaps, detergents, lubricants and cosmetics ingredients. The industry is a long-standing buyer of tallow and other lipid residues.
Open effluent pond: An uncovered lagoon where palm mill wastewater decays without oxygen, releasing large amounts of methane. It is the default practice at many mills.

P

Palm fatty acid distillate (PFAD): A by-product of refining crude palm oil, rich in free fatty acids. It is often treated as a residue, but it has established markets in feed, soap and oleochemicals and is tied to palm's land use.
Palm oil mill effluent (POME): The wastewater from palm oil mills. Its decay produces methane, and oil skimmed from it is traded as a low-value residue feedstock.
Paraffinic diesel: Diesel made of paraffins (alkanes) rather than a crude-oil mixture, meeting the European standard EN 15940. HVO and gas-to-liquids diesel are both paraffinic.
Peat (peatland): Waterlogged soil made of partly decayed plant matter, built up over thousands of years and holding very large carbon stocks. Southeast Asian tropical peat swamps are a major frontier of palm expansion.
Peat oxidation: The continuous release of CO₂ when drained peat is exposed to air and decomposes. It recurs every year for as long as the land stays drained. Estimates for drained tropical peat run from about 38 to 95 t CO₂ per hectare per year.
Permanence and reversal: Permanence is how long stored carbon stays out of the atmosphere. A reversal is its return, for example when tilled soil releases carbon or a forest burns.
Physical verification: Checking the material itself, through sampling, lab testing or site inspection, rather than only the paperwork.
Plot-level geolocation: Recording the exact coordinates of the farm or plantation plot where a feedstock was grown, so that buyers can check it against deforestation and peat maps.
Process CO₂ capture: Catching the CO₂ that a plant releases during chemical conversion and storing it. For HVO, the capturable stream comes from decarboxylation, which strips oxygen as CO₂.

R

RED (Renewable Energy Directive): The EU's main law for renewable energy, first adopted in 2009 and recast as RED II in 2018 and amended as RED III in 2023. It sets the EU lifecycle method that most European HVO claims rely on.
Rendering: Cooking animal by-products from slaughterhouses to separate fat (tallow) from protein meal and water. Renderers control much of the lowest-carbon HVO feedstock.
Residue: A material produced incidentally by a process that was not aimed at making it, such as tallow or tall oil. Residues sit between wastes and co-products and are often assigned zero upstream emissions in attributional rules.
Residue supply ceiling: The fixed upper limit on waste and residue supply, set by how much cooking, slaughter or refining occurs rather than by fuel prices. Extra fuel demand beyond it is met by crop oils.
RFS (Renewable Fuel Standard): The U.S. federal program, run by the EPA, that mandates annual volumes of renewable fuel in the transport supply. Its lifecycle analysis includes ILUC. Its 2018 grain sorghum oil pathway was the first U.S. regulatory use of displacement emissions.

S

Section 45Z (clean fuel production credit): A U.S. tax credit created by the Inflation Reduction Act of 2022 for low-emission transport fuel produced from 2025, scaled by carbon intensity. As amended in 2025, it uses the 45ZCF-GREET model, excludes ILUC for fuel produced after 2025 and restricts feedstocks to North America.
Soil carbon (soil organic carbon, SOC): Carbon stored in soil as decomposed plant and microbial material. Practices such as reduced tillage and cover crops can raise it, but gains are reversible, saturate over time and are hard to verify.
Soil N₂O (direct and indirect): Nitrous oxide emitted from fertilized soil. Direct emissions come from the field itself; indirect emissions arise after nitrogen escapes as ammonia gas (volatilization) or dissolves into water (leaching) and is converted elsewhere.
Soil-carbon credit: A reduction in reported fuel intensity claimed for farming practices that build soil carbon. U.S. policy now lets such practices feed into Section 45Z through USDA's feedstock carbon-intensity framework from 29 July 2026.
Steam methane reforming (SMR): The dominant industrial route to hydrogen: natural gas reacts with steam at high temperature to give hydrogen and CO₂. Without capture it produces grey hydrogen.
Stoichiometric estimate: A calculation based on the fixed ratios in which atoms combine in a chemical reaction. It gives a physical ceiling.
Straight-chain paraffins (n-paraffins): Saturated hydrocarbon molecules whose carbon atoms form a single unbranched line. Hydrotreated fats yield mostly chains of 15 to 18 carbons, which burn cleanly but turn waxy in the cold.
Sustainable aviation fuel (SAF): Jet fuel made from non-fossil sources, such as HEFA from fats and oils. Because it draws on the same lipid feedstocks as HVO, the two compete directly for limited residues.
System boundary: The line that defines which processes a lifecycle assessment includes and which it leaves out. Moving the boundary changes the result.
System expansion (substitution method): Avoiding allocation by giving the main product a credit for the product its co-product displaces elsewhere. Soybean meal, for example, earns a credit for the feed protein it replaces. The result depends heavily on which product is assumed to be displaced and can even turn negative.

T

Tallow (animal fat): Rendered fat from cattle, sheep or other livestock. Its HVO carries a RED typical value of 16.0 g CO₂e/MJ, but its consequential footprint depends on the category and on what replaces it.
Tier 1 exposure: THR's shorthand for a Tier 2 pathway that would fall into Tier 1 under a different, credible set of assumptions, most often GLOBIOM-type ILUC values or consequential accounting.
Tier 1, Tier 2, Tier 3 and Tier 4: THR's four-step classification that separates "lower than fossil diesel" from "carbon-neutral", defined against the 94 g CO₂e/MJ fossil comparator. It is a THR framework, not a regulatory category. See the table
Tonne-kilometre (tkm): Moving one tonne of freight one kilometre. Freight emissions per tkm let fleets compare fuels on the work actually done.
Traceability: The ability to follow a feedstock back to its verified origin through every transaction. It is the main defense against fraudulent or mislabeled waste feedstock.
Transesterification: The reaction that makes FAME: fats react with methanol to form methyl esters and glycerol. It uses less energy than hydroprocessing for clean oils, which can make biodiesel lower-emission than HVO for oilseed feedstocks.
Transport & Environment (T&E): A Brussels-based advocacy group campaigning for cleaner transport, and a frequent critic of crop-based and imported waste-based biofuels.
Triglyceride: The main molecule in fats and oils: three fatty-acid chains attached to a glycerol backbone.

U

Ultra-low-sulfur diesel (ULSD): Fossil diesel with sulfur content below 15 parts per million (U.S.) or 10 ppm (EU), the standard road diesel today.
Union Database for Biofuels (UDB): The European Commission's central database, rolled out from 2024, that records biofuel and feedstock transactions from origin to market so that the same batch cannot be claimed twice or relabeled.
USDA feedstock carbon-intensity framework: The U.S. Department of Agriculture's framework for quantifying farm-level feedstock emissions, including practices that build soil carbon, so they can lower a fuel's 45Z carbon intensity. It took effect on 29 July 2026.
Used cooking oil (UCO): Oil and fat already used for frying, collected from restaurants and food processors. It is the lowest-carbon mainstream HVO feedstock on attributional accounting, at about 14 g CO₂e/MJ, but supply is limited and prone to mislabeling.

V

Vegetable-oil substitution: The tendency of vegetable oils to replace one another in global markets because they are largely interchangeable. Extra demand for any one oil is ultimately met, at the margin, by the cheapest, which is usually palm.
Virgin vegetable oil: Oil from fresh crops that has not been used. Its price is a benchmark for waste oils.
Volumetric energy density: Energy per litre of fuel. HVO holds about 34 MJ per litre against about 36 for fossil diesel, so slightly more litres are needed for the same work.

W

Waste oil (waste-oil HVO): HVO made from wastes and residues such as used cooking oil and animal fats rather than crop oils. Waste status is attested by certification bodies and earns lower default emissions and extra policy support.
Waste status: The official recognition that a material is a waste or residue rather than a product, which unlocks favorable accounting and incentives. Because the label is valuable, it is a target for fraud.
Well-to-tank, tank-to-wheel and well-to-wheel: Fuel lifecycle stages. Well-to-tank covers production and delivery to the vehicle; tank-to-wheel covers combustion in the engine; well-to-wheel is both together.

Y

Yield-price elasticity: How strongly crop yields respond to higher prices, through more fertilizer or better management rather than more land. A higher elasticity means less land clearing and lower ILUC. CARB calls it the most influential GTAP-BIO parameter, tested across 0.05 to 0.35.