Biodiesel is made by chemically reacting fats or vegetable oils with an alcohol.
The main reaction is called transesterification. It converts triglycerides in oils or fats into fatty-acid alkyl esters, which form biodiesel, while glycerol is produced as a by-product. Methanol is commonly used, although other alcohols are possible.
Feedstocks can include soybean oil, rapeseed oil, used cooking oil, and animal fats. The final fuel can be blended with petroleum diesel or used in suitable diesel engines, depending on fuel standards and manufacturer guidance.
Biodiesel is different from renewable diesel. Biodiesel retains an ester-based chemical structure, while renewable diesel is processed to resemble petroleum diesel more closely. Bioethanol is also different: it is an alcohol fuel commonly produced by fermenting sugars or starches.