Biodiesel is a form of diesel fuel derived from plants or animals and consisting of long-chain fatty acid  esters. It is typivally made by chemically reacting lipids such as animal fat (tallow) soybean oil or some  other vegetable oil with an alcohol, producing a methyl, ethyl or propyl ester.

Unlike the vegetable and waste oils used to fuel converted diesel engines, biodiesel is a drop-in bio-fuel,  meaning it is compatible with existing diesel engines and distribution infrastructure. Biodiesel can be used alone or blended with petro diesel in any proportions. Biodiesel blends can also be used as heating oil. 100% biodiesel is referred to as B100.