E85 and Flex-Fuel Vehicles: What They Are and How They Differ

E85 is a gasoline-ethanol blend containing 51% to 83% ethanol, depending on geography and season, and it can be used only in flex-fuel vehicles (FFVs). A flex-fuel vehicle is designed to run on gasoline, on E85, or on any blend between them up to 83% ethanol. Because ethanol holds less energy per gallon, miles per gallon fall on E85 even though the vehicle runs normally.

Key takeaways

• E85 is approved only for flex-fuel vehicles. The AFDC states that E85 is not approved for use in gasoline-only models.
• fueleconomy.gov says FFVs typically get about 15% to 27% fewer miles per gallon on E85 than on gasoline.
• Ordinary pump gasoline is usually E10 (up to 10% ethanol) and is approved for any gasoline vehicle.
• E15 is approved for model year 2001 and newer light-duty conventional vehicles, according to the AFDC.

Ethanol blends at a glance

Blend	Ethanol content	Who can use it
E10	10% ethanol, 90% gasoline	Approved by the EPA for any conventional gasoline vehicle; sold in every state
E15	10.5% to 15% ethanol	Model year 2001 and newer light-duty conventional vehicles
E85	51% to 83% ethanol	Flex-fuel vehicles only

The AFDC adds that most U.S. gasoline contains up to 10% ethanol, that E15 requires a misfueling mitigation plan to reduce the risk of older vehicles refueling with it, and that E85 is the one that qualifies as an alternative fuel under the Energy Policy Act of 1992 (E10 and E15 do not).

How to tell whether a vehicle is an FFV

fueleconomy.gov lists several clues. Most manufacturers started putting yellow gas caps on FFVs from the 2008 model year (2006 for General Motors). Some vehicles with capless fuel inlets show a yellow filler ring. You may also find fuel door labels or body badges reading E85, Flex-Fuel or FFV, and the owner’s manual states which fuels are compatible. If you are unsure, check the manual before using E85. The AFDC notes that many vehicle owners do not realize their car is an FFV.

Why fuel economy drops on E85

Ethanol contains less energy than gasoline. The AFDC says denatured ethanol (98% ethanol) contains about 30% less energy than gasoline per gallon, and fueleconomy.gov concludes that FFVs typically get about 15% to 27% fewer miles per gallon on E85. fueleconomy.gov attributes the reduction to ethanol’s lower energy density. The AFDC notes that ethanol has a higher octane number than gasoline and that many FFVs have improved acceleration on higher ethanol blends, and fueleconomy.gov also reports no loss in performance on E85, and in some cases more torque and horsepower.

What that means for cost per mile

Because a gallon of E85 takes you fewer miles, its price per gallon has to be compared against the lower MPG, not on its own. The arithmetic: if a vehicle gets 20 MPG on gasoline and 15% fewer MPG on E85, that is 17 MPG on E85, and the E85 price per gallon must be lower than the gasoline price by about 15% for the cost per mile to be equal. At 27% fewer MPG, the break-even gap is larger. E85 prices vary by place and time; check station prices and the AFDC station locator rather than assuming a gap.

For the general cost formula, see how annual fuel cost is calculated. You can enter your own E85 price and a reduced MPG in the fuel cost calculator.

How labels treat FFVs

For the label’s rating slider, EPA guidance says flex-fuel vehicles are rated on gasoline operation, like gasoline vehicles, and that its summary fuel economy ranges do not include the MPG of FFVs operating on E85. For the units, see what is MPG and MPGe.

Finding E85

fueleconomy.gov refers readers to the AFDC for E85 station availability, and the AFDC’s station locator is the place to look. Availability varies by region, so check your area before counting on it.

What not to do

Do not put E85 in a vehicle that is not an FFV. The AFDC states that E85 is not approved for use in gasoline-only models. Do not assume a vehicle that “runs on regular” is flex-fuel either. For octane questions on ordinary gasoline, see regular vs premium gas, and for the other liquid fuel in this series, see diesel and DEF basics.