The Department of Energy definition of alternative fuels states that they are substantially non-petroleum and yield energy security and environmental benefits. Alternative fuels are substitutes for conventional engine fuels such as gasoline and diesel.
The U.S. Energy Policy Act defines alternative fuels as the following:
In January 2001 the Biodiesel Final Rule made it possible for fleets to earn EPAct credits for use of biodiesel blends of at least 20%. This rule does not make B20 (a 20% blend of biodiesel with diesel) an alternative fuel, but gives one credit for every 450 gallons of pure biodiesel used in biodiesel blends.