The United States produced an estimated 13.8 billion gal. of ethanol in 2011. Five companies produced more than 40% of that total.

ADM - This Decatur, Ill.-based grain and oilseed processor produces 1.75 billion gal./yr. It operates seven ethanol production plants. Visit  www.adm.com.

Poet - Headquartered in Sioux Falls, S.D., Poet produces 1.6 billion gal./yr. at 27 production plants. Visit www.poet.com.

Valero Energy Corporation - This company produces 1.2 billion gal./yr. at 10 production plants. It is headquartered in San Antonio, Texas. Visit www.valero.com.

Green Plains Renewable Energy - Headquartered in Omaha, Neb., Green Plains produces 740 million gal./yr. at different production plants. Visit www.gpreinc.com.

Flint Hills Resources LP - This Wichita, Kan., company produces 440 million gal./yr. at four production plants. Visit www.fhr.com.