Ethanol in gas: what E10, E15 and ethanol-free really mean for your car

Almost all regular gas in the U.S. is E10 — up to 10% ethanol. Some stations sell E15 (15%) or E85 (flex-fuel vehicles only). Here's what that actually does, without the myths.

Ethanol lowers MPG a little

Ethanol holds about a third less energy per gallon than gasoline, so E10 typically costs you roughly 3% fewer miles per gallon than ethanol-free gas — small, but real. E15 is a bit more. The EPA MPG figures on this site are measured on standard test fuel, so your real-world number shifts with the blend you pump.

Is E15 safe for my car?

The EPA approves E15 for most 2001-and-newer light-duty vehicles, but some automakers advise against it, and it can void warranties on older cars, motorcycles, boats and small engines. If your owner's manual or fuel door doesn't okay E15, stick to E10. We won't tell you it's fine for your specific engine — your manual will.

Where to find ethanol-free gas

Ethanol-free ("pure") gas exists, usually as a higher-priced option, and is popular for small engines, classics and boats. The community-run pure-gas.org maps stations that sell it. Expect to pay more per gallon; whether the small MPG gain is worth it depends on the price spread that day.

General fuel-chemistry facts; vehicle approval per EPA E15 guidance. Always confirm with your owner's manual.