Fuel nozzle representing how to identify a flex-fuel vehicle and whether it can use E85

Flex Fuel Vehicles: How to Tell If You Can Use E85

February 23, 2026 10 min read

Quick Summary E85 is a high-ethanol fuel that can only be used in flex-fuel vehicles (FFVs). FuelEconomy.gov provides a practical checklist for identifying an FFV (labels, fuel door markings, and common cues like a yellow fuel cap).

Do not assume a vehicle can use E85 — verify FFV compatibility first.
FuelEconomy.gov explains where to look (owner's manual, labels, and the fuel filler area).
E85 can reduce MPG compared to gasoline, so compare cost per mile, not price per gallon.

What We Know (Sourced)

FuelEconomy.gov explains that flex-fuel vehicles are designed to operate on gasoline, E85 (a mix of gasoline and ethanol), or any blend in between. It also states that not all vehicles can use E85 and provides guidance on how to identify an FFV.

FuelEconomy.gov's ethanol blends page provides baseline estimates for MPG changes by blend, including that E85 can reduce fuel economy compared to gasoline.

Bottom line: Compatibility comes first. Cost savings (if any) comes second, and should be evaluated using cost per mile.

How to Tell if Your Vehicle Is Flex Fuel

FuelEconomy.gov suggests multiple ways to identify an FFV. In practice, you can use a checklist approach:

Check the owner's manual for approved fuel types (E85 / flex-fuel language).
Look for labels in the fuel door area or under the hood indicating ethanol compatibility.
Check the fuel cap: FuelEconomy.gov notes many FFVs have a yellow fuel cap (though not every FFV will).
Confirm via trusted sources if uncertain (dealer documentation, manufacturer resources, or FuelEconomy.gov vehicle listings).

If you cannot confirm FFV capability, do not use E85.

How E85 Changes MPG and Cost Per Mile

FuelEconomy.gov provides baseline estimates of fuel-economy impacts for ethanol blends and notes that higher ethanol blends can reduce fuel economy compared to gasoline.

That means the price-per-gallon comparison is incomplete. Use cost per mile:

Cost per mile = price per gallon ÷ MPG

Compute once using your measured MPG on gasoline, and again on E85

What's Next

Confirm FFV compatibility using the owner's manual and labeling before you try E85.
Measure your MPG for a few tanks on E85 if you want a real cost-per-mile comparison.
Budget for commuting using weekly and monthly totals. Related: commute gas cost.

Comparing fuel costs?

Convert MPG and prices into cost per mile and annual fuel cost.

Try the Cost Per Mile Calculator

Frequently Asked Questions

Can I use E85 in a regular gasoline car?

No. FuelEconomy.gov states that not all vehicles can use E85. E85 should only be used in flex-fuel vehicles designed for it.

How do I know if my car is an FFV if I don't have the manual?

FuelEconomy.gov suggests checking the fuel door area for labels, under-hood labels, and common cues like a yellow fuel cap. If you cannot confirm compatibility, do not use E85.

Is E85 always cheaper per mile?

Not necessarily. FuelEconomy.gov estimates E85 reduces fuel economy compared to gasoline, so the price per gallon must be low enough to offset the MPG loss. Cost-per-mile math gives the correct comparison.