Ethanol works as a fuel in much the same way as gasoline; it is burned in a combustion reaction to release energy. In automobiles, ethanol is usually mixed with gasoline. Most cars can run on an ethanol-gasoline mixture with 10% ethanol (E10)—but to use an 85% ethanol mixture (E85) requires a specially designed system. Ethanol burns much cleaner than gasoline, making it less hazardous to the environment. It is also a renewable resource that can be produced by growing crops, so it has the potential to reduce dependence on foreign oil sources.