E85, E15, CNG, propane autogas and biodiesel compared
What each fuel is, which vehicles can use it, and how to compare prices fairly on an energy basis.
Alternative fuels are sold in different units and hold different amounts of energy, so the pump price alone misleads. The Department of Energy’s quarterly Alternative Fuel Price Report converts each to a gasoline gallon equivalent (GGE) so they can be compared.
Ethanol blends
- E10 is ordinary U.S. gasoline, up to 10% ethanol.
- E15 (up to 15% ethanol) is approved by EPA for 2001-and-newer cars and light trucks and all flex-fuel vehicles.
- E85 (51–83% ethanol) is for flex-fuel vehicles only. It usually costs less per gallon but delivers fewer miles per gallon.
Natural gas
CNG is sold per GGE and is common in transit buses, refuse trucks and some fleets. LNG is sold per diesel gallon equivalent (DGE) for heavy trucks.
Propane autogas
The same fuel as home heating propane, sold at vehicle fueling sites for school buses, delivery vans and forklifts. Each gallon holds about a quarter less energy than gasoline.
Biodiesel and renewable diesel
- B20 (20% biodiesel) works in most diesel engines; check the manufacturer’s approval. B100 needs compatible equipment and care in cold weather.
- Renewable diesel is chemically similar to petroleum diesel and is used as a drop-in replacement, mainly in California today.
Current prices are on the alternative fuels page; for electricity see EV charging cost by state.