Biofuels glossary
The vocabulary of biofuels, defined in plain language — from carbon intensity and RINs to FAME, cellulosic and the blend levels at the pump.
Biofuels carry a dense vocabulary drawn from chemistry, agriculture and fuel regulation. This glossary defines the terms used across this reference in plain language — from the fuels themselves (ethanol, biodiesel, renewable diesel) and the feedstocks they start from, to the production processes (fermentation, transesterification, hydrotreating) and the policy machinery (the RFS, RINs, carbon intensity and low-carbon fuel standards) that governs them. Each definition is intended to stand on its own; the fuller explanations live in the ethanol, biodiesel, advanced-fuels and policy sections.
- Advanced biofuel
- A renewable fuel other than corn-starch ethanol that achieves at least a 50% lifecycle greenhouse-gas reduction (RFS definition).
- Bagasse
- The fibrous residue left after sugarcane is crushed; burned at mills to power ethanol production.
- Biodiesel (FAME)
- A diesel fuel made from oils and fats by transesterification into fatty-acid methyl esters; used in blends with petroleum diesel.
- Biomass
- Material from recently living organisms — crops, residues, wood, oils, wastes — used as biofuel feedstock.
- Blend wall
- The practical ceiling on ethanol use when most gasoline is E10 and the fleet is built around it.
- Carbon intensity (CI)
- Lifecycle greenhouse-gas emissions of a fuel per unit of energy (gCO₂e/MJ); the basis for low-carbon fuel standards.
- Cellulosic biofuel
- Fuel made from cellulose, hemicellulose or lignin in non-food biomass; must meet a 60% GHG-reduction threshold under the RFS.
- E10 / E15 / E85
- Gasoline blends containing 10%, 15% and 51–83% ethanol respectively; E85 requires a flex-fuel vehicle.
- Ethanol
- Ethyl alcohol (C₂H₅OH) made by fermenting sugars and starches; the most widely used biofuel, blended into gasoline.
- Feedstock
- The raw biomass a biofuel is made from — e.g. corn, sugarcane, soybean oil, used cooking oil, crop residues.
- Flex-fuel vehicle (FFV)
- A vehicle built to run on gasoline, E85, or any blend in between, adjusting automatically to ethanol content.
- First-generation biofuel
- Fuel made from food crops — corn and sugarcane ethanol, vegetable-oil biodiesel.
- Hydrotreating (HVO)
- A process that reacts fats and oils with hydrogen to make renewable diesel chemically near-identical to petroleum diesel.
- LCFS
- Low Carbon Fuel Standard — a regulation setting a declining carbon-intensity target for transport fuels, with tradable credits.
- Renewable diesel
- A drop-in diesel made by hydrotreating fats and oils; usable at high blend levels, unlike FAME biodiesel.
- RFS
- Renewable Fuel Standard — the US federal mandate requiring set volumes of renewable fuel to be blended each year.
- RIN
- Renewable Identification Number — the tradable credit used to track and enforce RFS compliance.
- SAF
- Sustainable aviation fuel — jet fuel made from renewable or waste feedstocks rather than crude oil.
- Transesterification
- The reaction of oils/fats with an alcohol and catalyst to produce biodiesel (FAME) and glycerin.
- Renewable Volume Obligation (RVO)
- The share of renewable fuel an obligated refiner or importer must blend in a given year under the RFS.
Glossary: common term questions
What is the difference between biodiesel and renewable diesel?
Both are made from oils and fats, but biodiesel (FAME) is produced by transesterification and is chemically different from petroleum diesel, so it is used in blends; renewable diesel is produced by hydrotreating and is chemically near-identical to petroleum diesel, so it is a drop-in fuel.
What is the difference between the RFS and the LCFS?
The Renewable Fuel Standard (RFS) mandates volumes of renewable fuel; the Low Carbon Fuel Standard (LCFS) sets a declining carbon-intensity target and lets any fuel compete on its carbon score. One is volume-based, the other carbon-based.
What does “carbon intensity” actually measure?
It measures a fuel’s lifecycle greenhouse-gas emissions per unit of energy — counting how the feedstock is grown, processed, transported and burned — usually in grams of CO₂-equivalent per megajoule (gCO₂e/MJ).
What is the difference between first-generation and cellulosic biofuels?
First-generation biofuels are made from food crops (corn, sugarcane, vegetable oils); cellulosic biofuels are made from non-food plant fibre such as crop residues, grasses and wood, generally with lower lifecycle carbon and land-use impact.
What is a RIN?
A Renewable Identification Number is the tradable credit used to track and enforce the US Renewable Fuel Standard — one is generated for each gallon of renewable fuel and retired by obligated parties to prove compliance.