Alternative fuels are any fuel other than gasoline that is used to power motor vehicles of any size. The following fuels qualify under the U.S. Energy Policy Act of 1992 as alternative fuels: methanol, ethanol, blends of 85 percent or more of alcohol with gasoline, natural gas, propane, pure biodiesel (B100), and renewable diesel (R99). The U.S. Department of Energy may designate other fuels as alternative fuels, provided that the fuel is substantially non-petroleum, yields substantial energy security benefits, and offers substantial environmental benefits.
In 2005, Congress enacted the Renewable Fuel Standard (RFS) that set minimum requirements for the use of renewable fuels, including ethanol. In 2007, the RFS renewable fuel use targets were set to rise steadily to a level of 36 billion gallons by 2022.
Resource: Clean Cities Fuel Price Comparisons April 2016