What E85 is, and which cars can use it
fueleconomy.gov describes E85, also called flex fuel, as "an ethanol-gasoline blend containing 51% to 83% ethanol, depending on geography and season." It's sold at its own pump, usually priced below regular.
Only flex-fuel vehicles (FFVs) can use it. fueleconomy.gov says FFVs "are specially designed to run on gasoline, E85, or any mixture of the two." Your owner's manual is the surest way to check. Check the owner's manual before you fill up. WXYZ Detroit warns that in a car that isn't set up for it, E85 can cause lean running conditions and engine damage.
Why E85 gets fewer miles per gallon
Ethanol simply holds less energy. fueleconomy.gov says ethanol "contains about one-third less energy than gasoline," and that FFVs running on E85 "get roughly 15% to 27% fewer miles per gallon than when operating on regular gasoline." The exact drop depends on the vehicle and on how much ethanol is in the blend that season.
That lost mileage is the whole question. A cheaper gallon that takes you fewer miles can cost more per mile than a pricier gallon that takes you further.
Your break-even E85 price
E85 costs the same per mile as regular when its price is lower by the same share as your mileage drop:
Break-even E85 price = regular price × (1 − MPG drop)
- Regular: an example $3.50 ÷ 20 MPG = $0.175 a mile
- E85 at a 27% drop: 20 × 0.73 = 14.6 MPG, and an example $2.90 ÷ 14.6 = about $0.199 a mile
- Over 11,500 miles: $2,012.50 on regular vs $2,284.25 on E85, so regular saves $271.75
- Break-even: $3.50 × 0.73 = about $2.56 a gallon for E85
At the low end of the range, a 15% drop, the break-even price is $3.50 × 0.85 = about $2.98, and the same $2.90 E85 would save you a little. That's why your own vehicle's drop matters. If you know your MPG on both fuels, enter the real difference.
GasBuddy's Patrick De Haan offers a quick rule that lands in the same place: "if E85 is at a 20% discount or greater compared to gasoline, it may be worth it."
What real-world tests found
The best-known head-to-head test is old but still useful. Edmunds drove a 2007 Chevrolet Tahoe on both fuels and got 18.3 MPG on gasoline and 13.5 MPG on E85, "a 26.5 percent worse" result. At that time's prices, E85 cost 22.8 percent more to drive the same distance. The performance difference was "small enough to go unnoticed by most drivers," and CO2 output dropped by only about 0.5 percent.
Prices have changed a great deal since then, so the cost result doesn't carry over, but the mileage drop sits right inside fueleconomy.gov's 15% to 27% range.
What drivers are saying
- The mileage drop is the first thing owners mention. A commenter in a 2017 r/cars thread put the drop at roughly 20% to 25% and said E85 only saves money when its price is cut by more than the mileage you lose, which is the same break-even math the calculator above does (Reddit, r/cars). That is one commenter's estimate, not a test, and it sits in the same range as the fueleconomy.gov figure above.
- Some owners say it isn't worth it. A video from the channel Purple Collar Life is titled "E85 is a waste of money! Flex Fuel vs Regular Unleaded MPG and Cost". The video is about 15 minutes long and we only confirmed its title, so we can't say what else it covers.
- Others have saved when the gap was wide. In a 2022 WXYZ report, a police department said it had bought about 5,000 gallons of E85 in 30 days and saved $6,500 over that stretch.
- Availability can be a problem. The same WXYZ report says E85 can run in short supply and that some stations have the pump shut off.
The opinions split along the price gap. When E85 is much cheaper than regular, owners report savings. When the gap is small, the lost mileage wins. We couldn't read the full Reddit thread for this page, so the quote comes from its preview in search results. To find E85 near you, use the Department of Energy's Alternative Fuels Data Center station locator.
Cedrick Reese built this page because E85's lower pump price is easy to see, while its lower mileage isn't. The ethanol content, energy and mileage figures come from the Department of Energy's fueleconomy.gov, the break-even rule from GasBuddy as reported by WXYZ, and the road test from Edmunds, with its age noted. The calculator compares cost per mile, the only fair way to compare two fuels with different mileage, and the worked example above is checked by hand. The page is reviewed when fueleconomy.gov updates its ethanol guidance, and both prices shown are only examples.
E85 questions
Is E85 worth it?
Only when it's cheap enough. Flex-fuel vehicles get roughly 15% to 27% fewer miles per gallon on E85, according to fueleconomy.gov, so E85 has to cost at least that much less per gallon than regular to break even. GasBuddy's Patrick De Haan says it may be worth it at a 20% discount or more.
Can I switch back and forth between E85 and regular gas?
In a flex-fuel vehicle, yes. fueleconomy.gov says flex-fuel vehicles are designed to run on gasoline, E85 or any mixture of the two. In a car that isn't flex-fuel, don't use E85 at all.
Can I mix E85 and regular 87?
Only in a flex-fuel vehicle, which can run on any mixture of gasoline and E85. In other cars, E85 can cause lean running conditions and engine damage, so check your owner's manual first.
What are the disadvantages of E85?
Lower mileage is the big one: roughly 15% to 27% fewer miles per gallon in flex-fuel vehicles. It only works in flex-fuel vehicles, fewer stations sell it, and the savings depend on the price gap with regular.
Is E85 the same as 93 octane?
No. E85 is an ethanol blend, not a grade of gasoline. It does carry a high octane rating, which the Iowa Renewable Fuels Association lists at 100 to 105, but only flex-fuel vehicles can use it. Don't put it in a regular car to get higher octane.
More fuel tools
Work out a trip's fuel cost with the fuel cost calculator, or your fuel bill for the year with the gas budget calculator. Driving in liters? The metric fuel cost calculator works in L/100 km and price per liter.
Sources
Last reviewed: October 4, 2026.
- fueleconomy.gov, Ethanol
- WXYZ Detroit, The pros and cons of using E85 over regular gas, and how to check if your car can use it
- Edmunds, E85 vs. Gasoline Comparison Test
- Iowa Renewable Fuels Association, E85 FAQs
- Reddit r/cars, ELI5: Pros and Cons of using E85 fuel on flex fuel vehicles
- Purple Collar Life on YouTube, E85 is a waste of money! Flex Fuel vs Regular Unleaded MPG and Cost
- U.S. Department of Energy, Alternative Fuels Data Center station locator