B20 is a diesel fuel blend containing 6% to 20% biodiesel mixed with conventional petroleum diesel. It’s one of the most widely used biodiesel blends in the United States, popular with fleets and commercial vehicles because it offers a meaningful reduction in emissions without requiring engine modifications. The “B” stands for biodiesel, and the “20” indicates the maximum percentage of biodiesel in the mix.
What’s Actually in B20
The biodiesel portion of B20 is made by chemically reacting fats or oils with an alcohol, typically methanol. This process transforms the raw material into a fuel that burns cleanly in diesel engines. The remaining 80% or more of B20 is standard petroleum diesel, which is why the blend behaves so similarly to regular diesel at the pump and in the engine.
The fats and oils used as raw materials come from a wide range of sources. Soybean oil is one of the most common feedstocks in the U.S., but producers also use waste cooking oil from restaurants, animal fats like beef tallow and chicken fat, canola oil, and palm oil. Waste-based feedstocks are increasingly favored because they’re cheap, abundant, and don’t compete with food production. The choice of feedstock can vary by region and season, but the finished biodiesel must meet the same quality standards regardless of what it was made from.
B20 sold commercially in the U.S. must meet ASTM D7467, a quality standard that governs blends containing 6% to 20% biodiesel. This specification ensures the fuel performs reliably across different engines and conditions.
Energy Content Compared to Regular Diesel
B20 contains slightly less energy per gallon than standard diesel, but the difference is smaller than most people expect. One gallon of B20 holds about 126,700 BTU, compared to 128,488 BTU for low-sulfur diesel. That works out to roughly 99% of the energy in a gallon of conventional diesel, translating to a 1% to 2% reduction in fuel economy. In practical terms, most drivers won’t notice the difference on a single tank, though it can add up over high-mileage fleet operations.
Engine Compatibility and Warranties
B20 works in standard diesel engines without any hardware changes. You don’t need a special fuel system, different injectors, or an engine conversion. For context, the lower blend B5 (up to 5% biodiesel) is approved for use in all diesel vehicles sold in the U.S. B20 has broader manufacturer support than higher blends but isn’t universally approved across every engine.
Many major engine manufacturers explicitly approve their engines for B20 use. The key step before switching is checking whether your specific engine model and year are on the approved list. Clean Fuels Alliance America maintains a list for heavy-duty vehicles, and the Engine Technology Forum provides one for light-duty diesel models. If your engine is approved, using B20 won’t void your warranty. If it isn’t listed, using B20 could create warranty complications if a fuel-related issue arises.
Why Fleets Choose B20
B20 hits a practical sweet spot. Lower blends like B5 reduce emissions only modestly. Higher blends like B100 (pure biodiesel) can cause cold-weather gelling, degrade certain rubber seals in older engines, and have a much shorter shelf life. B20 avoids most of these problems while still delivering a noticeable environmental benefit. It reduces lifecycle carbon emissions compared to petroleum diesel because the plants and waste materials used to produce the biodiesel absorbed carbon dioxide while growing or during their original use.
For fleet managers, the appeal is straightforward: B20 can be stored in the same tanks, pumped through the same infrastructure, and burned in the same engines as regular diesel, with minimal operational changes. Many municipal bus systems, school districts, and delivery fleets use B20 as a low-friction way to meet sustainability goals.
Storage and Shelf Life
B20 doesn’t last as long in storage as petroleum diesel. Research from the National Renewable Energy Laboratory found that B20 blends remain stable for up to four months when the biodiesel component meets standard oxidation stability requirements. After that window, the biodiesel portion can begin to degrade, forming deposits and acids that may clog filters or corrode fuel system components. By comparison, B5 blends can stay stable for up to 12 months under the same conditions.
If you’re storing B20, keep it in clean, sealed tanks away from excessive heat and moisture. Fuel turnover matters: buying only what you’ll use within a few months is the simplest way to avoid degradation issues. For seasonal equipment that sits idle for long stretches, a lower biodiesel blend or straight diesel is a safer choice for the fuel system.
Cold Weather Considerations
Biodiesel has a higher cloud point than petroleum diesel, meaning it starts to form waxy crystals at warmer temperatures. In B20, this effect is diluted but not eliminated. During cold months, some fuel suppliers adjust the blend ratio downward (closer to B6 or B10) or use cold-flow additives to prevent gelling. If you live in a region with harsh winters, it’s worth confirming that your fuel supplier accounts for seasonal temperature swings in their B20 formulation.