The two most common types of biofuels are ethanol and biodiesel .
Ethanol is an alcohol, the same found in beer and wine.
Ethanol is mostly used as a fuel additive to cut down a vehicle's carbon monoxide and other smog-causing emissions. Biodiesel, however, is not an alcohol. It's an ester, which is similar to vinegar. Many vegetable oils, animal fats, algae, or even recycled cooking greases are used to produce biodiesel. It is used as a diesel additive to reduce vehicle emissions or in its pure form to fuel a vehicle.