Ethanol is a renewable alcohol fuel made from plant sugars. It is the same molecule found in alcoholic drinks, but fuel-grade ethanol is denatured with additives to make it undrinkable. Most ethanol comes from corn in the United States and sugarcane in Brazil. It is blended with gasoline, usually at 10 percent, to boost octane and cut emissions.

Production uses fermentation. Yeast converts sugars into alcohol. Distillation concentrates it. The leftover grain becomes animal feed, which improves the economics. Cellulosic ethanol, made from crop residues and grasses, avoids using food crops, but has struggled to scale.

Ethanol has supporters and critics. It reduces oil imports and supports farm income. It also competes with food production, uses fertilizer and water, and delivers only modest greenhouse gas savings compared with gasoline. The net benefit depends on how the feedstock is grown and processed.

Common feedstocks

• Corn
• Sugarcane
• Wheat
• Cellulosic biomass
• Sugar beet