Ethanol is a fuel made from corn and other plant materials that can be blended with gasoline to reduce costs.
On January 21, 2011, the Environmental Protection Agency (EPA) partially approved two partial waivers to allow the introduction of E15 or 15-percent ethanol for use in model year 2001 and newer light duty vehicles. Most gasoline service stations currently sell E10 or 10-percent ethanol.
Now that E15 has been approved for sale, some gasoline service stations may dispense both E10 and E15 from the same pump. Motorists could run into a problem when they fill up with E10 after an E15 buyer because they could get as much as a quart of residual E15. While this is not a big deal if you purchase a lot of gasoline, those that purchase small quantities of gasoline (for motorcycles or lawn mowers) could damage their engines and void their warranties. To prevent such problems, EPA will require purchasers of E15 to buy a minimum of four gallons from any pump that sells E15.
E15 has a lower energy density than ethanol-free gasoline; the lower energy density will lower your gas mileage. E10 lowers your vehicle fuel efficiency 3 to 4 percent compared to ethanol free gasoline, and the efficiency of E15 will be even lower.