Yes, most cars already run on biofuel to some degree. Nearly all gasoline sold in the United States contains 10% ethanol (called E10), and most diesel engines can handle biodiesel blends up to 20% without any modifications. Whether your car can run on higher concentrations depends on the type of engine, the type of biofuel, and whether the vehicle was built to handle it.
Gasoline Cars and Ethanol Blends
Every standard gasoline car on the road today is designed to run on E10, the baseline fuel at most gas stations. A higher blend called E15, which contains 15% ethanol, is available at some pumps and is approved for cars from model year 2001 and newer. The EPA has been issuing rolling summer waivers throughout 2025 to keep E15 available year-round, since it’s normally restricted during warmer months due to evaporation concerns.
Going beyond E15 requires a flex-fuel vehicle (FFV). These cars and trucks can run on anything from pure gasoline up to E85, a blend containing 51% to 83% ethanol. Flex-fuel vehicles use a sensor in the fuel line that measures the ethanol concentration by detecting changes in the fuel’s electrical properties. That reading goes to the engine’s computer, which adjusts how much fuel gets injected and when the spark plugs fire. The result is a clean burn regardless of what’s in the tank. Millions of FFVs are on U.S. roads, and many owners don’t even realize their vehicle is flex-fuel capable (check for a yellow gas cap or a sticker inside the fuel door).
The tradeoff with ethanol is energy density. Ethanol contains less energy per gallon than gasoline, so fuel economy drops. With E10, the decrease is roughly 3%. With E85, the drop is more significant, typically 15% to 27% fewer miles per gallon. You’ll fill up more often, though E85 is usually cheaper per gallon.
Diesel Cars and Biodiesel
Diesel engines have even more flexibility with biofuels. Low-level biodiesel blends like B5 (5% biodiesel, 95% petroleum diesel) meet ASTM fuel standards and are approved for any diesel engine. B20 blends work in most current diesel engines without modifications, and many manufacturers explicitly approve their use.
Pure biodiesel, called B100, is a different story. It acts as a solvent, scrubbing deposits that petroleum diesel left behind in fuel tanks and lines. That sounds helpful, but those loosened deposits flow downstream and clog fuel filters. If you switch to high-concentration biodiesel, expect to replace your fuel filters frequently during the first few tanks until the system cleans itself out. Engines built since 1994 with biodiesel-compatible hoses and gaskets can generally handle B100, but you should confirm with your manufacturer.
Cold weather is biodiesel’s biggest weakness. The fuel begins to form waxy crystals at higher temperatures than petroleum diesel, and those crystals clog fuel lines and filters. At low enough temperatures, biodiesel can gel completely and stop flowing. Winter-grade additives help, and lower blends like B5 or B20 are far less affected, which is why most cold-climate drivers stick with modest blends during winter months.
Renewable Diesel: The True Drop-In Fuel
Renewable diesel is chemically identical to petroleum diesel, even though it’s made from plant oils, animal fats, or waste grease. Because the manufacturing process (called hydrotreating) rearranges the molecular structure to match conventional diesel, renewable diesel can be used at 100% concentration, labeled R100, in any diesel engine with zero modifications. It doesn’t gel as easily in cold weather, doesn’t act as a solvent that loosens old deposits, and can travel through the same pipelines and storage tanks as petroleum diesel.
Biodiesel, by contrast, can’t be stored or transported in standard petroleum infrastructure. It has to move by rail, barge, or truck. This logistical limitation is one reason renewable diesel has been growing faster as a petroleum diesel replacement, even though biodiesel has been around longer.
What Biofuels Do to Your Engine Long-Term
The main concern with biofuel over time is its effect on rubber seals, O-rings, and gaskets. Research on elastomer degradation shows that fuels containing ethanol, methanol, and butanol cause the most swelling and breakdown in rubber components. Certain seal materials absorb the biofuel and gain mass, which changes their shape and compromises the seal. This is why older vehicles not designed for ethanol blends can develop fuel leaks or injector problems when exposed to higher concentrations.
Hydrotreated vegetable oil (the base of renewable diesel) did not significantly degrade elastomer seals in testing, which further explains why it’s considered the most engine-friendly biofuel option. For standard ethanol blends at E10 or E15, modern vehicles use fuel system materials specifically chosen to resist this kind of degradation, so it’s not a practical concern for cars built in the last two decades.
How Much Do Biofuels Cut Emissions?
Biofuels reduce greenhouse gas emissions because the plants used to make them absorbed carbon dioxide while growing, partially offsetting the carbon released when the fuel burns. The actual reduction depends heavily on the fuel type and how the feedstock was grown and processed.
Corn ethanol, the most common U.S. biofuel, offers a moderate reduction. Current U.S. corn ethanol production avoids an estimated 45 million metric tons of CO2-equivalent emissions per year. Biodiesel and renewable diesel show stronger potential per gallon, with some fuel pathways achieving a 50% or greater reduction in carbon intensity compared to petroleum fuels. By 2035, biodiesel and renewable diesel together are projected to reduce diesel-category emissions by about 8%.
The biggest gains come from advanced biofuels made from non-food sources like agricultural waste, wood chips, or dedicated energy crops. These cellulosic biofuels have the lowest carbon footprint, though commercial production is still scaling up. The EPA’s proposed renewable fuel standards for 2026 call for 1.3 billion ethanol-equivalent gallons of cellulosic biofuel, a small but growing share of the overall 24 billion gallon renewable fuel target.
Which Biofuel Works for Your Car
If you drive a standard gasoline car, you’re already using biofuel every time you fill up with E10. You can safely use E15 if your car is 2001 or newer. Anything above that requires a flex-fuel vehicle.
If you drive a diesel, blends up to B20 are a straightforward swap at any station that carries them. Renewable diesel (R100) is the easiest high-concentration option since it requires no engine changes and performs like petroleum diesel in all conditions. Pure biodiesel is possible but demands more attention to filter maintenance, seal compatibility, and seasonal temperatures.
For drivers interested in reducing their carbon footprint without buying a new vehicle, biofuel blends are one of the simplest available options. The infrastructure is already in place, compatibility with existing engines is well established, and the fuel is sold at thousands of stations across the country.