The Effects of Ethanol on Fuel Mileage

The hidden cost of ethanol.

Most gasoline powered cars run on straight gasoline although these vehicles can also safely run on an ethanol blend consisting of 10 percent ethanol and 90 percent gasoline. Known as E10 fuel or gasohol, many service station pumps across the nation offer this blend. A placard should be posted on the pump alerting you that E10 fuel is in use.

Fuel Economy

Ethanol, however, is less fuel efficient than straight gasoline. The U.S. Environmental Protection Agency reports that cars fueled with E10 will typically see a drop in fuel efficiency by 3 or 4 percent. What that means is if your car is averaging 30 mpg, you will most likely average about 29 mpg with E10 fuel. Certainly, that doesn’t make for much of a difference for one fill up, but over the course of a year you’ll pay for it.

Some vehicles are “flex fuel” rated and can run on either straight gasoline or consume E85 fuel which is 85 percent ethanol and 15 percent gasoline. These vehicles have modified fuel lines and a fuel tank in addition to certain computer diagnostic changes that enable the car to run efficiently. E85 is corrosive and not suited for cars that haven’t been modified accordingly.

Cost & Performance

The drawback for E85 fuel is that it is approximately 25 to 30 percent less efficient than straight gasoline. That means your 30 mpg car might get as low as 21 mpg when fueled solely with E85. Performance isn’t affected, but fuel efficiency is a big hindrance to the widespread acceptance of this fuel.

Cost is another factor and unless this fuel is priced correspondingly less than gasoline, drivers will pay more for fuel. For example, when regular gasoline is averaging $3.25 per gallon, the E85 should retail for $2.25 per gallon or less to make it worthwhile for drivers to fill up. Unfortunately, except for some pumps in corn growing regions of the country (midwest) this fuel is hard to find and pricey.


Should you avoid ethanol? You may not be able to do so with E10, but if your vehicle is flex fuel capable and the cost of the fuel is not correspondingly lower to justify the loss in efficiency, than your fueling costs will skyrocket. As of this writing, the cheapest ethanol fuel is about $2.50 per gallon in Minnesota according to the website. So, even in corn-growing regions ethanol cannot offer to you the value you need to justify fueling with E85.