Chemical conversion involves the use of chemical interactions to transform biomass into other forms of usable energy. Transesterification is the most common form of chemical conversion and it is a chemical reaction in which fatty acids from fats, greases, and oils are bonded to alcohol. The process reduces the viscosity of the fatty acids and makes them combustible. A common end-product of transesterification is biodiesel, as well as glycerin and soaps. Biodiesel can be converted from almost any tree oil, animal fat or tallow, or bio-oil (soybean oil).