Renewable fuels are any liquid or gaseous fuels produced from biological materials, waste streams, or renewable electricity rather than from petroleum or other fossil sources. They’re designed to replace or blend with conventional gasoline, diesel, and jet fuel while producing fewer greenhouse gas emissions over their full lifecycle. The category is broad, ranging from the corn ethanol already blended into most gasoline sold in the U.S. to synthetic fuels made entirely from captured carbon dioxide and water.
The Main Types of Renewable Fuels
Renewable fuels fall into several distinct categories, each defined by what it’s made from and how much it cuts emissions compared to petroleum.
- Conventional biofuel (corn ethanol) is the most common renewable fuel in the U.S. It’s produced by fermenting the starch in corn kernels and must reduce lifecycle greenhouse gas emissions by at least 20% compared to a 2005 petroleum baseline.
- Biomass-based diesel covers biodiesel and renewable diesel made from vegetable oils, animal fats, or used cooking oil. These fuels must cut emissions by at least 50%.
- Cellulosic biofuel is made from the tough, fibrous parts of plants (stalks, wood chips, agricultural residues) rather than from food crops. It carries the strictest emissions requirement: a 60% reduction.
- Advanced biofuel is a catch-all for any non-corn-starch renewable fuel that achieves at least a 50% emissions reduction. This includes sugarcane ethanol, biogas, and several newer fuel pathways.
These categories come from the U.S. Renewable Fuel Standard, the federal program that requires refiners to blend increasing volumes of renewable fuel into the nation’s transportation fuel supply each year.
Generations of Biofuel
Scientists also sort renewable fuels by “generation,” which is really a way of describing what raw material goes in.
First-generation biofuels use food crops. Corn and wheat provide starch for ethanol in North America and Europe. Sugarcane does the same job in South America. Biodiesel comes from food-grade rapeseed, soy, or palm oil. These fuels are the easiest to produce at scale, but they compete directly with the food supply, a tension that flared during the 2007–2008 global food price crisis and hasn’t fully resolved.
Second-generation biofuels sidestep that problem by using agricultural residues, wood waste, food-industry byproducts like wheat bran, used cooking oil, and animal fats. Non-food crops grown on marginal land, such as the drought-resistant shrub jatropha, also fall into this group. Because these feedstocks don’t require converting farmland away from food production, they avoid the core criticism of first-generation fuels.
Third- and fourth-generation biofuels use algae or genetically engineered microorganisms, though commercial-scale production remains limited.
How Renewable Fuels Are Made
The production method depends on the fuel. Ethanol is made through fermentation: microbes break down sugars or starches into alcohol, which is then distilled and purified. It’s the same basic chemistry behind beer and wine, scaled up to industrial volumes.
Biodiesel uses a chemical reaction called transesterification, where vegetable oils or animal fats are combined with an alcohol to produce a fuel that works in diesel engines. Renewable diesel takes a different approach: it uses hydrogen to process the same oils and fats into a fuel that is chemically identical to petroleum diesel. That distinction matters because renewable diesel can replace petroleum diesel without any engine modifications or blending limits, while biodiesel typically needs to be blended at lower percentages.
Other production methods include gasification (heating biomass at extreme temperatures to produce a gas that can be converted into liquid fuel) and pyrolysis (rapidly heating biomass without oxygen to break it down into oil-like liquids).
E-Fuels and Green Hydrogen
Not all renewable fuels come from plants or waste. A newer category, sometimes called electrofuels or e-fuels, is made by combining green hydrogen with captured carbon dioxide.
The process starts with water electrolysis: renewable electricity from wind, solar, or hydropower splits water into hydrogen and oxygen. That hydrogen is then reacted with CO2 captured from industrial exhaust or the atmosphere to produce synthetic versions of methane, methanol, or liquid hydrocarbons. Because the carbon released when these fuels burn is the same carbon that was captured to make them, the net emissions can approach zero.
E-fuels are especially relevant for sectors that can’t easily electrify. Aviation is the clearest example. Sustainable aviation fuel, or SAF, currently has 11 certified production pathways approved by the international standards body ASTM. The Department of Energy projects that two of those pathways will dominate near-term production: one based on processing fats and oils, expected to supply about 66% of SAF by 2030, and another that converts alcohols into jet fuel, accounting for roughly 23%.
Drop-In Fuels and Engine Compatibility
One of the practical questions people have about renewable fuels is whether they work in existing engines. The answer depends on the fuel. Ethanol is typically blended with gasoline at 10% (E10) or 15% (E15), and most modern cars handle these blends without modification. Higher blends like E85 require flex-fuel vehicles.
Renewable diesel and renewable gasoline are what the industry calls “drop-in” fuels. Renewable gasoline is chemically identical to petroleum gasoline and meets the exact same fuel specification, so it works in any existing gasoline engine and can flow through existing pipelines and pumps. Renewable diesel has the same compatibility advantage for diesel engines. This is a significant practical benefit: no new vehicles, no new fueling stations, no new supply chain.
Biodiesel, by contrast, has different chemical properties from petroleum diesel and is typically used in blends rather than as a full replacement.
Environmental Tradeoffs
Renewable fuels reduce greenhouse gas emissions compared to petroleum, but the size of that reduction varies widely. Corn ethanol clears a relatively low bar of 20% lifecycle emissions reduction. Cellulosic biofuels made from waste wood or crop residues can achieve 60% or more. E-fuels powered entirely by renewable electricity and using captured CO2 can theoretically approach carbon neutrality.
The environmental picture isn’t purely positive, though. Large-scale production of first-generation biofuels has driven real harm. In Malaysia and Indonesia, rainforests have been cleared for vast palm oil plantations to supply biodiesel refineries, creating a palm oil shortage and destroying ecosystems. In parts of Africa, rice and maize farmers have been displaced from their land to make way for sugarcane and jatropha plantations. Proposals in Benin alone have targeted 300,000 to 400,000 hectares of wetlands for palm oil production. These land-use changes can release so much stored carbon that they cancel out the emissions benefits of the fuel itself.
The shift toward second-generation feedstocks, waste oils, agricultural residues, and non-food crops grown on marginal land, is partly a response to these problems. So is the growing interest in e-fuels, which don’t require agricultural land at all.
How Much Renewable Fuel the U.S. Requires
The U.S. Renewable Fuel Standard sets annual blending targets that refiners must meet. For 2026, the EPA has proposed requirements of 24.02 billion ethanol-equivalent gallons of total renewable fuel, including 7.12 billion gallons of biomass-based diesel and 1.30 billion gallons of cellulosic biofuel. Those numbers are set to tick upward in 2027, to 24.46 billion total gallons. The cellulosic target has been the hardest to hit: the EPA has repeatedly had to reduce it because production hasn’t kept pace with original projections.
These mandates have made the U.S. one of the largest renewable fuel markets in the world and created a financial incentive structure that drives investment across all the fuel types described above.