Visit Website →
← Back to blog

Flex Fuel vs. Regular Gas: Costs, Mileage and Which to Use

October 21, 2026
Flex Fuel vs. Regular Gas: Costs, Mileage and Which to Use

Flex fuel (E85) usually costs less per gallon than regular gas, but it gives you fewer miles per gallon, so it is not always cheaper to drive on. A flex fuel vehicle (FFV) can run on regular gasoline, E85, or any mix of the two. A gasoline-only car can never use E85. If you are shopping for a used car, the real questions are whether the vehicle is an FFV, whether E85 is sold near you, and whether the math works for your driving.

Elmwoodautosalesri
Choose a Used Car With Confidence
Elmwood Auto Sales offers thoroughly inspected used vehicles and a low-pressure buying experience in Providence.
Explore used vehicles

TL;DR

  • Flex fuel vehicles can run on regular gasoline, E85, or any blend of the two. Standard gasoline-only cars cannot use E85.
  • E85 typically cuts fuel economy by 15% to 27%, so a lower price per gallon does not guarantee a lower cost per mile.
  • Check the label inside the fuel filler door, not just the badge, to confirm a car is an FFV.
  • In Rhode Island, E85 is hard to find, so most local FFV owners will fill up with regular gas anyway. Don't pay extra for flex fuel capability you can't use.

Table of Contents

What is flex fuel, and how is it different from regular gas?

Flex fuel is the common name for E85, a blend of gasoline and denatured ethanol. The EPA describes E85 as containing up to 85 percent ethanol, the highest-ethanol fuel blend on the market, and says it can only be used in vehicles specifically designed for it. The Alternative Fuels Data Center notes that the actual ethanol content in E85 ranges from 51% to 83%, depending on geography and season.

Regular gas is not ethanol-free either. The U.S. Energy Information Administration reports that most finished motor gasoline sold in the United States is about 10% ethanol by volume. That blend is called E10, and every gasoline car on the road is built to handle it. The difference between the pump labeled "regular" and a pump labeled "E85" is concentration, and only specially designed vehicles can handle the higher one.

What is flex fuel, and how is it different from regular gas? — overview diagram

What makes a flex fuel vehicle different from a regular car?

FFVs are close to ordinary cars. According to fueleconomy.gov, apart from a few engine and fuel system modifications, they are identical to gasoline-only models. The fuel system uses materials that tolerate ethanol, and the engine control module detects the blend in the tank and adjusts accordingly.

This is also why many owners do not know they have one. The same source says an FFV looks like its gasoline-only twin. Fueleconomy.gov reports there were over 20.9 million FFVs on U.S. roads as of 2022.

A flex fuel vehicle is also different from a bi-fuel vehicle. A bi-fuel vehicle carries two fuels in separate tanks. An FFV has one tank and one fuel system that accepts gasoline, ethanol blends, or a mix.

Can a flex fuel car use regular gas?

Yes. Regular gasoline is always an option in an FFV. You can also switch back and forth. Fueleconomy.gov says you can move between E85 and regular gasoline at any time, and the engine control module adjusts to whatever mixture is in the tank.

This matters for a used-car shopper. An FFV is not a special-fuel car that strands you when E85 is unavailable. It is a gasoline car with extra capability. If you never use E85, you will drive it exactly like any other vehicle.

What happens if you put E85 in a regular car?

This is the costly mistake. E85 must never go into a gasoline-only vehicle. Standard fuel systems are not designed for its high ethanol content, and fueleconomy.gov warns it can damage the fuel system and engine. Repairs from misfueling are generally not something a standard warranty covers, so confirm the vehicle is labeled for E85 before you fill up.

If you have already put E85 in a car that is not an FFV, do not drive on it. Ask a certified technician what to do before you start the engine, since the right step depends on the vehicle and how much was added.

How can you tell if a car is a flex fuel vehicle?

There are three quick checks, in order of reliability:

  1. Open the fuel filler door. Per fueleconomy.gov, the most reliable sign is a label there that mentions E85 or flex fuel capability. Some FFVs also have a yellow fuel cap.
  2. Look for a badge on the rear. Badges such as "FFV," "Flex Fuel" or "E85" are common but not on every vehicle, and they can be removed.
  3. Check the owner's manual or the vehicle's build details. The manual states which fuels the engine is approved for.

The Alternative Fuels Data Center also points readers to fueleconomy.gov for help identifying an FFV. On a used car, do not assume. The same engine can be flex fuel in one model year and gasoline-only in another, so verify the specific vehicle you are buying.

Is E85 really cheaper than regular gas?

Per gallon, usually yes. Per mile, often no. Ethanol carries about one-third less energy than gasoline, and E85 contains much more of it than the E10 in regular pumps. Fueleconomy.gov puts the typical drop in fuel economy on E85 at 15% to 27% compared with regular gasoline.

Looking at price alone misses that. Kelley Blue Book, citing AAA, reported that in late March 2026 the national average for E85 was about $3.14 per gallon, roughly 85 cents below regular unleaded. That puts regular at about $3.99 in the same comparison. Here is what that looks like in practice:

ScenarioFuel priceMileage vs. gasolineCost to go the distance 1 gallon of regular would take you
Regular gas$3.99100%$3.99
E85, 15% fewer mpg$3.1485%about $3.69
E85, 21% fewer mpg$3.1479%about $3.97
E85, 27% fewer mpg$3.1473%about $4.30

The figures in the last column are our own arithmetic: the E85 price divided by the share of mileage you keep. They use the national averages above, which are a snapshot and will not match your local pump.

The pattern is simple. E85's discount at the pump was about 21% in that comparison. If your vehicle loses less than 21% of its mileage on E85, you come out slightly ahead. If it loses more, regular gas costs less per mile. Because the loss ranges from 15% to 27%, the answer depends on the specific engine. A rule of thumb that works: E85 needs to be at least 15% to 27% cheaper per gallon than regular, depending on your vehicle, before it saves money.

E85 discount versus flex-fuel mileage loss

To run the numbers for your own car, fill up on each fuel and record the miles per gallon you actually get. Then divide price per gallon by mpg for each. The lower figure is your cheaper fuel. Fueleconomy.gov frames this as an economic choice for FFV owners rather than a mechanical one, which is the right way to think about it.

What are the pros and cons of flex fuel?

Pros

  • Lower price per gallon. E85 is often cheaper at the pump, as the AAA figure above shows.
  • Flexibility. You can fill up with whatever is available and cheaper that day.
  • Performance. Fueleconomy.gov says FFV drivers typically see no loss in performance on E85, and some vehicles even produce more torque and horsepower.
  • Environmental case. The EPA says E85 can reduce dependence on imported oil and lower greenhouse gas emissions compared with petroleum-derived gasoline.

Cons

  • Lower fuel economy. The 15% to 27% drop means more fill-ups and a shorter range per tank.
  • Limited availability. E85 is not sold at every station, as Kelley Blue Book points out.
  • Savings are not guaranteed. As the table shows, cost per mile can end up higher than regular gas.
  • Misfueling risk. If you drive more than one vehicle, mixing up which one takes E85 can cause expensive damage.

Can you even buy E85 in Rhode Island?

This is the question that matters most for a Providence-area buyer. One third-party station tracker lists no public E85 stations in Rhode Island, and says the closest is in Seekonk, Massachusetts, about five miles from the state line. Station lists change, so confirm current locations with the Alternative Fuels Data Center station locator before planning around E85.

If that holds, the practical picture is clear. A flex fuel vehicle bought here will run on regular gas nearly all the time. E85 would mean a trip over the border, and the extra miles can erase whatever you save per gallon. For most local drivers, flex fuel capability is neutral: harmless, but not a reason to pay more for a car.

Does flex fuel matter when you buy a used car?

Only a little, and it should not outweigh the things that do decide long-term cost. When you compare used vehicles, these usually matter more:

  • Inspection results and vehicle history. A clean history report and a thorough inspection say more about reliability than the fuel label does.
  • Mileage. Our guide on why to be careful with high mileage used cars walks through what to check.
  • Engine choice. Trucks and SUVs often offer more than one engine, and the choice affects fuel cost and towing. See our comparison of V6 vs. V8 engines and our look at diesel vs. gas trucks for five-year costs.
  • Financing terms. A lower payment can save more than any fuel strategy. Our breakdown of biweekly vs. monthly car payments shows how the payment schedule changes what you pay.

If two vehicles are otherwise equal and one is an FFV, the FFV is a fine choice. It does everything the gasoline-only version does, with one extra option you may or may not use. Do not pay a premium for it, and do not rule out a gasoline-only car you like.

What does a dealership with no sales commission think about this?

Here is our view at Elmwood Auto Sales. We are a used car dealership in Providence, and we don't run on commission-based sales tactics, so our staff has no reason to push a feature just because it sounds good. Flex fuel is a good example. It is a real capability, but for most buyers in Rhode Island it is a minor one.

What we would tell a friend is this. Read the fuel filler door on any car you are considering, and ask us if the label is unclear. Decide on the car's condition, history and total monthly cost, not on a badge. Then run your own cost-per-mile numbers if E85 is ever convenient for you. We inspect the vehicles we sell, and we think a buyer who understands the car, including what fuel it takes, makes a better decision and is more likely to be happy with it years later.

One rule applies whatever you buy: if you share a household with more than one vehicle, make sure everyone knows which ones can use E85 and which cannot.

— Elmwood

Looking for a reliable used vehicle in Providence?

If you are comparing fuel types because you are shopping for a used car, SUV or truck, start with our current used inventory. If you are not sure what suits your budget or credit, you can apply for used car financing online, or tell our Car Finder what you need. Have a vehicle to move on? You can trade in or sell your car with us.

FAQ

Can I put normal gas in a flex fuel car?

Yes. A flex fuel vehicle runs on regular gasoline as well as E85 or any mix of the two. You do not need to use E85 at all. Many FFV owners never do.

What is the downside of flex fuel?

The main downside is lower fuel economy. Fueleconomy.gov reports a typical 15% to 27% drop on E85 compared with regular gasoline. E85 can also be hard to find, especially in Rhode Island. Because of those two things, it does not always save money.

Can I switch back and forth between E85 and regular gas?

Yes, at any time. The engine control module detects the mixture in the tank and adjusts. You do not have to run the tank empty first.

What happens if I put flex fuel in a regular car?

E85 can damage the fuel system and engine of a gasoline-only vehicle, and repair costs may not be covered by warranty. Do not start the engine if you realize the mistake at the pump or soon after. Call a certified technician for advice before driving.

Is E85 better for the environment?

It can be. The EPA says E85 can lower greenhouse gas emissions and reduce reliance on imported oil. The size of the benefit depends on how the ethanol is produced.

Sources