A substance or any material that can be used to provide power for an engine or which can be burned in air to release energy: Fuels, such as gasoline are made mostly of hydrocarbons (carbon and hydogen molecules).

A source of energy that is not diesel or petroleum-based: A variety of alternative fuels include:

• Methanol.
• Denatured ethanol, and other alcohols.
• Fuel mixtures containing 85 percent or more by volume of methanol, denatured ethanol, and other alcohols with gasoline or other fuels; such as, natural gas.
• Liquefied petroleum gas (propane).
• Hydrogen.
• Coal-derived liquid fuels.
• Fuels (other than alcohol) derived from biological materials (biofuels, such as soy diesel fuel).
• Electricity (including electricity from solar energy).

Any liquid source of energy obtained from a renewable biological resource suitable as a diesel fuel substitute or diesel fuel additive or extender: Biodiesel fuels are typically made from oils, such as soybeans, rapeseed, or sunflowers, or from animal tallow.

Biodiesel fuel can also be made from hydrocarbons derived from agricultural products: such as, rice hulls.

Any solid, gaseous, or liquid fuel obtained from biomass: Biomass fuel may be in its natural form (wood or peat) or from a commercially produced form (ethanol from sugarcane residue or diesel fuel from waste vegetable oils).