E85 is a blend of ethanol and gasoline that contains between 51% and 83% ethanol, with the remainder being conventional gasoline. The name suggests a fixed 85% ethanol mix, but the actual ratio shifts depending on where you live and the time of year. It’s sold at designated pumps and can only be used in vehicles specifically built to handle it, known as flex fuel vehicles (FFVs).
What’s Actually in E85
The ethanol in E85 is the same type of alcohol found in alcoholic beverages, though it’s produced industrially, mostly from corn in the United States. Blended with gasoline, it creates a fuel that burns differently than the regular gas you’d put in a standard car.
The blend percentage isn’t fixed at 85% ethanol, despite the name. Fuel producers adjust the ratio seasonally. In warmer months, the ethanol content runs higher, closer to 83%. In winter, they dial it back toward 51% and increase the gasoline portion. This seasonal adjustment exists because ethanol doesn’t vaporize as easily as gasoline in cold temperatures. Adding more gasoline to the winter blend helps the fuel ignite reliably when the engine is cold. Even with these adjustments, cold starts on E85 remain harder than on straight gasoline. Research from SAE International found that to match gasoline’s cold-start performance, an engine running E85 needs roughly three times the amount of fuel injected during startup.
Higher Octane, Lower Energy
E85 has a significantly higher octane rating than regular gasoline. Standard pump gas in the U.S. is rated at 87 AKI (anti-knock index), while E85 typically lands between 100 and 105 AKI. Octane measures a fuel’s resistance to premature detonation, or “knock,” which can damage engines. This high octane rating is one reason E85 appeals to performance enthusiasts, since engines tuned for higher octane can run more aggressive timing and produce more power.
The tradeoff is energy content. A gallon of E85 contains only 73% to 83% of the energy found in a gallon of regular gasoline. That means your engine burns through more fuel to cover the same distance. In practical terms, expect your miles per gallon to drop by roughly 15% to 27% compared to running standard gas. If you normally get 30 mpg on regular fuel, you might see 22 to 25 mpg on E85. Whether the lower price per gallon at the pump offsets that fuel economy penalty depends entirely on local pricing.
Which Vehicles Can Use It
Only flex fuel vehicles are designed to run E85. These vehicles have fuel system components, including fuel lines, seals, and injectors, built from materials that resist ethanol’s corrosive properties. Their engine computers also automatically detect the ethanol percentage in the tank and adjust fuel injection and ignition timing accordingly. This is what makes them “flex” fuel: they can run on anything from standard gasoline to E85 or any mix in between.
You can usually identify a flex fuel vehicle by a yellow gas cap or a badge on the body that reads “Flex Fuel” or “E85.” Your owner’s manual will confirm compatibility. Putting E85 in a non-flex-fuel vehicle is a bad idea. The higher ethanol concentration can degrade rubber seals, corrode metal fuel system parts, and trigger check engine lights. A single accidental tank likely won’t cause permanent damage, but repeated use will.
Emissions and Environmental Impact
E85 produces less net carbon dioxide per mile than conventional gasoline. The key word is “net.” When ethanol burns, it releases CO2 just like gasoline does. But the corn or other crops used to make ethanol absorbed CO2 from the atmosphere while growing, partially offsetting those tailpipe emissions. An analysis by Argonne National Laboratory found that corn-based ethanol reduces lifecycle greenhouse gas emissions by an average of 40% compared to petroleum gasoline.
That figure accounts for the full production chain: farming, processing, transportation, and combustion. Critics point out that the environmental benefit shrinks when you factor in land use changes, fertilizer runoff, and the energy needed to grow and process corn. The 40% reduction is a national average, and actual numbers vary by how and where the ethanol is produced.
Storage and Shelf Life
Ethanol is hygroscopic, meaning it pulls moisture from the surrounding air. This makes E85 more sensitive to storage conditions than regular gasoline. Over time, absorbed water can cause “phase separation,” where the ethanol and water settle to the bottom of the tank as a distinct layer, separate from the gasoline floating on top. An engine trying to run on that separated mixture will stumble or refuse to start.
Research conducted by the National Renewable Energy Laboratory tested ethanol-gasoline blends stored in small fuel tanks exposed to cycling temperatures and humidity. Even lower ethanol blends like E10 and E15 showed phase separation after 9 to 11 weeks under high-humidity conditions. E85, with its much higher ethanol content, is even more vulnerable. Fuel tank manufacturers generally recommend emptying the tank if a vehicle or piece of equipment will sit unused for three months or longer. If you only drive your flex fuel vehicle occasionally, keeping the tank full minimizes the air space where moisture can accumulate.
Where to Find It
E85 availability varies widely by region. The Midwest, where most U.S. ethanol is produced, has the densest network of E85 stations. In coastal states and rural areas outside the Corn Belt, finding a pump can require planning. The U.S. Department of Energy’s Alternative Fuels Station Locator is the most reliable way to find E85 stations near you or along a travel route. As of recent years, there are several thousand E85 stations across the country, but that’s still a fraction of the more than 150,000 gas stations nationwide.
Pricing at the pump generally runs lower per gallon than regular gasoline, but the gap fluctuates with corn prices, oil prices, and regional supply. Because of the fuel economy penalty, you need E85 to be at least 15% to 27% cheaper per gallon than regular gas just to break even on cost per mile. In many Midwestern markets, it clears that threshold. In other regions, the savings may be slim or nonexistent.