Ethanol. An alcohol produced from biomass (for example, corn, soybeans, and sugarcane) and used as a blending agent with gasoline to increase octane and cut down carbon monoxide and other smog-causing emissions. Almost all gas sold in the US includes ethanol.

Biodiesel. Typically made from new and used vegetable oils and animal fats, this fuel is used as a substitute for diesel. Unlike traditional diesel, biodiesel is non-toxic and biodegradable. Biodiesel is often used in combination with petroleum-based diesel but can also be used alone.