Ethanol (ethyl alcohol) is an alternative fuel fermented from corn, grains or agricultural waste or it is chemically extracted from ethylene (hydration). It is used primarily as a supplement to gasoline. Pure ethanol is not sold as a stand-alone fuel—it is commonly mixed with gasoline in varying percentages. For example, E85 is a common mixture: 85 percent ethanol, 15 percent gasoline. Most pump gasoline contains ethanol in much lower percentages. To burn high concentrations such as E85, vehicles have to be designed as flex-fuel vehicles to utilize the unique combustion characteristics and tolerate the corrosiveness of the alcohol.