E10 vs E15 vs E85: How Ethanol Blends Affect MPG and Cost

What We Know (Sourced)

FuelEconomy.gov provides an ethanol blends explainer that includes baseline fuel-economy impacts for common blends. It estimates E10 reduces fuel economy by about 3–4% and E15 by about 4–5%.

FuelEconomy.gov also states that E85 (a high-ethanol blend used in flex-fuel vehicles) can reduce fuel economy by about 15–27% compared to gasoline.

For E15 eligibility, FuelEconomy.gov states E15 is approved for use in model year 2001 and newer light-duty vehicles, and is prohibited in motorcycles, heavy-duty vehicles, and off-road engines.

How MPG Typically Changes by Blend

As ethanol percentage increases, the energy content per gallon of the fuel blend generally decreases. FuelEconomy.gov's baseline estimates are a practical way to set expectations:

• E10: about 3–4% lower fuel economy than gasoline.
• E15: about 4–5% lower fuel economy than gasoline.
• E85: about 15–27% lower fuel economy than gasoline.

The key is to avoid comparing fuels only by their posted price. If one fuel costs less per gallon but yields fewer miles per gallon, the correct comparison is cost per mile.

How to Compare Cost Per Mile Fairly

If you want a cleaner comparison metric, use cost per 100 miles (or gallons per 100 miles). Related: fuel cost per 100 miles and gallons per 100 miles.

Practical approach: If you can, run an A/B test. Use E10 for a few tanks, then E15 (if eligible) for a few tanks on a similar commute, and compare average MPG and cost per mile. Related: commute fuel budgeting.

Vehicle Eligibility and Labeling (E15 and E85)

Fuel choice isn't only about cost. It also depends on whether your vehicle is approved for that blend:

• E15: FuelEconomy.gov states it's approved for model year 2001+ light-duty vehicles, and prohibited in motorcycles, heavy-duty vehicles, and off-road engines.
• E85: Use only in flex-fuel vehicles (FFVs). FuelEconomy.gov provides guidance on how to identify FFVs (for example, a yellow gas cap or labels). Related: flex fuel vehicle identification.

What's Next

• If you're comparing prices at the pump: convert each option to cost per mile.
• If you're unsure about compatibility: verify your vehicle's fuel recommendations before using E15 or E85.
• If you want long-run savings: track MPG changes over multiple tanks, not a single fill-up.

If you're working on overall cost reduction, remember that driving style, idling, and maintenance can swamp small blend differences. Start here: maintenance checklist and aggressive driving.

Frequently Asked Questions