Biodiesel B20 is a fuel blend containing 6% to 20% biodiesel mixed with conventional petroleum diesel. It’s the most widely used biodiesel blend in the United States, offering a balance between lower emissions and full compatibility with most diesel engines. At roughly $3.74 per gallon, B20 typically costs about the same as regular diesel.
What’s in the Blend
The “B” stands for biodiesel, and the number indicates the maximum percentage of biodiesel in the mix. So B20 contains up to 20% biodiesel and at least 80% standard petroleum diesel. Other common blends include B5 (up to 5% biodiesel) and B100 (pure biodiesel). B20 must meet quality standards set by ASTM D7467, an industry specification that ensures the fuel performs reliably in diesel engines.
The biodiesel portion is made by chemically reacting vegetable oils or animal fats with an alcohol, usually methanol. More than 95% of the world’s biodiesel comes from edible oil crops like soybeans, canola, and palm. But it can also be produced from waste cooking oil, chicken fat, beef tallow, and dairy processing byproducts. These waste-based sources are increasingly popular because they don’t compete with food production.
Engine Compatibility and Warranties
Most major diesel engine and equipment manufacturers approve B20 for use in their products. Cummins approves B20 in its 2002 and later on-highway engines as well as a wide range of off-highway models, though it requires biodiesel sourced from BQ-9000 certified suppliers (an industry quality program). John Deere approves B20 in engines through its Tier 3 models, including all non-emissions-certified engines. Case IH approves B20 for more than 90% of models sold in the U.S. and Europe. Caterpillar uses a tiered approval system, supporting up to B30 depending on the equipment type.
The key requirement across manufacturers is that the biodiesel component meets the ASTM D6751 specification and the petroleum diesel meets ASTM D975. If you’re considering B20 for a specific vehicle or piece of equipment, check the owner’s manual. Some manufacturers, like Isuzu, have historically limited warranty coverage for biodiesel-related failures, approving only B5.
Energy Content and Fuel Economy
B20 contains about 126,700 BTUs per gallon, compared to roughly 128,500 BTUs per gallon for standard diesel. That’s about 1.4% less energy per gallon. In practice, this translates to a fuel economy drop of around 1% to 2%. A large-scale evaluation by the National Renewable Energy Laboratory tracked transit buses over 100,000 miles and found that B20 buses averaged the same 4.41 miles per gallon as diesel buses in everyday driving. Lab testing on those same buses revealed a roughly 2% reduction in fuel economy, consistent with the lower energy content. For most drivers, the difference is barely noticeable at the pump.
The lab tests also showed minor reductions in peak torque, but nothing that affected normal vehicle operation.
Emissions Benefits
The primary environmental appeal of B20 is lower emissions compared to straight petroleum diesel. On a lifecycle basis, B20 produces about 79.3 grams of CO₂ equivalent per megajoule of energy, compared to 93.0 for petroleum diesel. That’s roughly a 15% reduction in lifecycle greenhouse gas emissions. Particulate matter, the tiny soot particles linked to respiratory problems, drops by about 12% with B20. Hydrocarbon and carbon monoxide emissions also decrease, though the reductions are more modest at B20 concentrations.
These benefits come from the biodiesel portion of the blend. Because the plant oils and animal fats used to make biodiesel absorbed carbon dioxide while growing, burning them releases less net carbon than burning petroleum that’s been underground for millions of years.
Cold Weather Considerations
Biodiesel thickens in cold temperatures more readily than petroleum diesel. This is measured by three properties: the cloud point (when wax crystals first appear), the pour point (when the fuel stops flowing), and the cold filter plugging point (when it clogs a fuel filter). At B20 concentrations, the effect is much less dramatic than with pure biodiesel, but it still matters in cold climates.
Cold flow additives can improve performance by lowering the pour point and plugging point by several degrees. In areas with harsh winters, B20 is sometimes blended with a higher proportion of petroleum diesel during the coldest months, or cold flow improvers are added at the terminal. Underground storage tanks help, since soil temperatures stay more stable than air temperatures.
Storage and Maintenance Tips
B20 has a shelf life of eight months to a year when stored properly. Adding antioxidants and testing periodically helps maintain fuel quality over that window. The biggest enemy of stored biodiesel blends is water. If moisture accumulates at the bottom of a tank, bacteria and fungus can grow in the fuel, plugging filters and causing corrosion. Tanks should be dry before filling and checked regularly for water buildup.
One practical consideration when first switching to B20: biodiesel has mild solvent properties that can loosen deposits left behind by petroleum diesel in fuel tanks and lines. In older vehicles or equipment with years of buildup, this can cause fuel filters to clog during the first few tank fills. Replacing the fuel filter after the initial transition typically resolves the issue, and the cleaning effect is actually beneficial for the fuel system long term.
Price and Availability
B20 is widely available at fueling stations across the United States, particularly in agricultural states and along major freight corridors. As of late 2025, the national average price for B20 is $3.74 per gallon, identical to the national average for conventional diesel. Prices fluctuate with both petroleum markets and the cost of feedstocks like soybean oil, and federal or state tax credits for biodiesel can shift the economics in either direction. Many commercial fleets, transit agencies, and government vehicles use B20 as a straightforward way to reduce emissions without modifying engines or infrastructure.