Fossil fuels have been the primary source of transportation fuel in the United States. Increasing concern about global warming and energy security have prompted significant interest and funding for alternative transportation fuels.
The United States produced 13.9 billion gallons of ethanol from corn grain in 2011. The Energy Independence and Security Act of 2007 calls for 36 billion gallons of renewable fuels by 2022. Corn ethanol will make up 15 billion gallons; cellulosic and advanced biofuels will make up the remaining 21 billion gallons.