Biodiesel vs diesel in one paragraph: Biodiesel is a fuel made from vegetable oils, used cooking oil or animal fats; petroleum diesel is refined from crude oil. Pure biodiesel (B100) has about 7% less energy per gallon, a higher cetane number, far better lubricity, and 40–86% lower lifecycle greenhouse-gas emissions — but it gels at higher temperatures and doesn't store as long. Blended to B20, those trade-offs shrink to a 1–2% mileage difference that most drivers never notice, which is why B20 is what's actually sold at the pump.
Side-by-side
| Property | Petroleum diesel (ULSD) | B20 | B100 |
|---|---|---|---|
| Made from | Crude oil | 80% diesel + 20% biodiesel | Soy/canola oil, used cooking oil, tallow |
| Fuel spec | ASTM D975 | ASTM D7467 | ASTM D6751 |
| Energy (BTU/gal) | ~128,500 | ~126,700 | ~119,550 |
| Fuel economy vs diesel | — | 1–2% lower | ~7% lower |
| Cetane number | 40–45 typical (40 minimum) | Slightly higher | 47 minimum; often 50+ |
| Lubricity | Poor without additives | Excellent | Excellent |
| Cloud point | About −10°F to 10°F | 2–10°F higher than the base diesel | ~32°F (soy) to ~60°F (tallow) |
| Lifecycle GHG | Baseline | ~8–17% lower | 40–86% lower |
| Tailpipe PM, CO, HC | Baseline | Lower | Much lower (pre-DPF engines) |
| Storage life | 1–2 years | ~6–12 months | 3–6 months without stabilizer |
| Engine approval | Universal | Most post-2007 diesels; current Ford, GM, Ram | Few on-highway engines |
| Where sold | Everywhere | ~2,000 public U.S. stations | 23 public U.S. pumps |
Sources: AFDC Fuel Properties Comparison; DOE/NLR Biodiesel Handling and Use Guide; ASTM D975, D7467, D6751; Argonne GREET; station counts from AFDC, September 2026.
Energy content and MPG
Biodiesel molecules carry about 11% oxygen by weight. Oxygen helps the fuel burn cleanly but adds no energy, so a gallon of B100 holds roughly 119,550 BTU against about 128,500 for No. 2 diesel — around 7% less. Fuel economy follows energy content almost exactly.
- B5: 0.35% less energy. Unmeasurable.
- B20: 1–2% less. On a truck that gets 18 mpg, that's about 0.3 mpg, or roughly 5–10 fewer miles from a 30-gallon tank. Normal variation from wind, load and winter diesel is bigger than that.
- B100: about 7% less. You will notice it.
Power and torque scale the same way: no perceptible change at B20, a small loss at B100.
Cetane, lubricity and engine wear
Cetane measures how readily fuel ignites under compression. ASTM requires a minimum of 40 for diesel and 47 for B100, and real-world biodiesel often tests above 50. Higher cetane means shorter ignition delay — slightly quieter running and easier cold starts (as long as the fuel itself hasn't gelled).
Lubricity is where biodiesel clearly wins. Removing sulfur to make ultra-low-sulfur diesel also stripped out the compounds that lubricated injection pumps and injectors, so refiners now add lubricity improvers to meet spec. As little as 2% biodiesel restores lubricity to better-than-old-diesel levels, a finding documented in the DOE handling guide and one reason some states and fleets adopted B2–B5 early.
The solvent effect. Biodiesel is a mild solvent. In a vehicle that has run petroleum diesel for years, B20 loosens varnish and sediment in the tank and lines and carries it to the fuel filter. That's why Cummins, for one, tells operators to change fuel filters at half the normal interval for the first two changes after moving to B20. After that, intervals go back to normal. It isn't damage; it's housecleaning, and it's worth carrying a spare filter for the first few tanks.
Materials. B20 is compatible with the seals and hoses in essentially all diesel vehicles built since the mid-1990s. B100 can soften natural rubber and nitrile components in older fuel systems over time.
Cold weather
This is biodiesel's real weakness. All diesel fuel forms wax crystals when it gets cold enough; the temperature where that starts is the cloud point. No. 2 diesel typically clouds somewhere between −10°F and 10°F depending on the refinery's seasonal blend. Soy-based B100 clouds right around freezing, and tallow-based B100 can cloud near 60°F.
Blending dilutes the problem. B20's cloud point lands only 2–10°F above the diesel it's blended with, and the same anti-gel additives and No. 1 diesel blending used for winter diesel work on B20. In practice, cold-climate retailers handle it for you: in our station data, 638 of 1,997 public stations list “B20 in summer, B5 in winter,” mostly in Iowa, Minnesota and Illinois. If you fill up at a public pump in January, you're already getting the winter blend.
Emissions
Lifecycle carbon. Because the carbon in biodiesel was recently pulled from the air by a plant, its lifecycle greenhouse-gas footprint is far lower than fossil diesel's. Argonne National Laboratory's GREET model puts the reduction at roughly 40–69% for soybean and canola biodiesel once land-use change is counted, and 70–86% for used cooking oil and animal fats. B20 delivers about one-fifth of that.
Tailpipe. In older engines without particulate filters, EPA testing found B20 cuts particulate matter, carbon monoxide and unburned hydrocarbons by roughly 10–20%, with B100 cutting them by around half. NOx is the exception: older studies showed a small increase (about 2% at B20), while testing on modern engines shows little or no difference. On a 2011-or-newer truck with a DPF and SCR, the aftertreatment system does most of the cleanup with either fuel, so the tailpipe difference is small and the lifecycle carbon difference is the main benefit.
Cost
At retail, B20 usually prices within 5–20 cents a gallon of diesel, in either direction. The gap depends on feedstock prices (soybean oil, used cooking oil), the federal clean-fuel production credit, and state policy. Illinois exempts higher biodiesel blends from sales tax, Iowa gives retailers a per-gallon credit and a lower excise rate on B11+, and California's Low Carbon Fuel Standard subsidizes low-carbon fuels — which is why those states have most of the country's stations and often the best B20 prices. B99/B100 typically costs 50 cents to a dollar more than diesel.
Factor in mileage: at 1–2% lower fuel economy, B20 needs to be roughly 4–8 cents cheaper than $4 diesel to break even per mile.
Storage and shelf life
Diesel stores for a year or two in a clean, dry tank. Biodiesel oxidizes faster and holds more dissolved water, which also makes it friendlier to microbial growth. The DOE handling guide suggests using B100 within about six months unless it's treated with an antioxidant and tested; B20 is more forgiving, but Ford advises against leaving B20 in a vehicle tank for more than a month unused. For a daily driver none of this matters. For a generator, a boat, or a tractor that sits all winter, fill it with straight diesel (or B5) before storage.
Biodiesel is not renewable diesel
They're made from the same fats and oils, but they're different fuels. Biodiesel (FAME) is made by transesterification and is sold as a blend: B5, B20, B99. Renewable diesel (HVO, sometimes sold as R99 or R100) is made by hydrotreating, is chemically a hydrocarbon just like petroleum diesel, meets ASTM D975, and can be used at 100% in any diesel engine with no cold-weather or storage penalty. Renewable diesel has taken over much of the California and Oregon market for that reason, and the two are often sold blended together (for example R80/B20). AFDC has a good renewable diesel overview.
Which should you use?
- Modern diesel pickup or truck, driven regularly: B20 where it's convenient and priced right. You get better lubricity and a real carbon reduction for a mileage cost you won't notice. Check your engine's approved blend first.
- Pre-2007 diesel, European diesel car (VW/Audi TDI, Mercedes, BMW), or anything under a warranty that says B5: stick to regular pump diesel, which is already up to B5.
- Equipment that sits for months: straight diesel or B5 for storage.
- Extreme cold: whatever the local pump sells — retailers in cold states already drop to B5 in winter.
- B100: only with an engine approved for it, a climate that suits it, and a supplier you trust. See B100 and B99.
FAQ
Is biodiesel better than diesel?
For lubricity, cetane and lifecycle carbon emissions, yes. For energy content, cold-weather performance and storage life, no. At the B20 blend sold at most biodiesel pumps, the downsides are small: about 1–2% lower fuel economy and a slightly higher gel point.
Can I mix biodiesel and regular diesel?
Yes. They mix completely in any proportion, and you can switch back and forth between B20 and regular diesel from one fill-up to the next with no procedure. Just stay at or below the blend your engine maker approves.
Does biodiesel get worse mileage?
Slightly. B20 has 1–2% less energy per gallon than petroleum diesel, and B100 about 7% less. Fuel economy drops by about the same percentages.
Is biodiesel cheaper than diesel?
Sometimes. B20 typically sells within 5–20 cents per gallon of regular diesel, above or below, depending on feedstock costs and state incentives. It is most often cheaper in Illinois, Iowa and Minnesota.
Will biodiesel damage my engine?
Not at blends your manufacturer approves. B20 is approved in current Ford Power Stroke, GM Duramax and Ram Cummins pickups and most heavy-duty engines built since 2007. Expect to change the fuel filter early once or twice after switching, because biodiesel loosens old deposits in the tank.