Quick answer
For fleets, the four biofuels worth understanding are renewable diesel (RD), biodiesel, ethanol, and renewable natural gas (RNG). They differ in chemistry, blending limits, and infrastructure fit:
| Fuel | Chemistry | Where it fits | Drop-in? |
|---|---|---|---|
| Renewable diesel (R99/R100) | Hydrocarbon, hydrotreated fats/oils | Any diesel engine | Yes |
| Biodiesel (B5–B20, FAME) | Fatty acid methyl ester | Diesel engines, blended | Limited (blend-rate sensitive) |
| Ethanol (E10–E85) | Alcohol from corn/cane/cellulose | Gasoline, mostly passenger vehicles | E10 yes; E85 only flex-fuel |
| Renewable natural gas (RNG) | Biogas upgraded to pipeline-quality methane | CNG/LNG fleets | Yes, drop-in for CNG/LNG |
Renewable diesel
RD is the most fleet-friendly option for diesel operators. It meets ASTM D975, runs in any diesel engine, has no blending cap, and typically delivers 60–80% lifecycle CO₂ reduction. California is the most mature market because of the Low Carbon Fuel Standard. See the renewable diesel vs. petroleum diesel guide for the deeper comparison.
Biodiesel
Biodiesel (FAME) is typically blended at B5–B20. Above B20, OEM approvals narrow and cold-weather behavior gets harder to manage without additives. Per-gallon energy content is slightly lower than petroleum diesel; expect a small MPG penalty. Lifecycle CO₂ reductions depend on feedstock and blend rate.
Ethanol
Most U.S. gasoline already contains 10% ethanol (E10). E15 is approved for many post-2001 light-duty vehicles. E85 is only for flex-fuel vehicles and is mainly relevant to consumer fleets in the Midwest. Ethanol lowers per-gallon energy content, so MPG drops accordingly — the per-mile cost picture depends on the spread between gasoline and ethanol pump prices.
Renewable natural gas (RNG)
RNG is biogas (from landfills, dairies, wastewater) upgraded to pipeline-quality methane. It is a drop-in for CNG and LNG vehicles, which means fleets already operating natural gas trucks can switch to RNG without engine changes. Lifecycle CO₂ can be very low — and in some cases negative — when dairy and landfill feedstocks are used.
What to ask suppliers
- What is the lifecycle carbon intensity (gCO₂e/MJ) of the specific batch?
- What standard does it meet (ASTM D975 for RD, ASTM D6751 for biodiesel)?
- Are LCFS or RFS credits transferred or retained?
- What is the supply commitment — months, years, take-or-pay?
- For RD and RNG, does the OEM warranty cover unrestricted use?
How to model the economics
Per-mile cost is the right lens. Use the Fleet TCO model to test scenarios with different fuel prices and credits. For an EV vs. liquid-fuel comparison on the same vehicle profile, the EV vs Gas Cost Calculator handles the energy side; pair it with the TCO model for ownership totals.
About these numbers
Carbon intensities and blending limits cited reflect CARB, EPA, and ASTM published guidance current as of 2025. Verify with your fuel supplier and OEM for specific equipment and jurisdiction.
