Biodiesel is a renewable fuel that can be made from triglyceride esters in oil crops such as rape seed. The oil is reacted with methanol in the presence of an acid or alkali catalyst to form a mixture of methyl esters which can be used with little or no modification in diesel engines. Biodiesel is cheaper than diesel obtained from crude oil and can be home-made using oil from restaurants.Biodiesel is a methyl or ethyl ester of a fatty acid. The process of making biodiesel is known as trans-esterification. Methanol or ethanol can be used in the presence of sodium or potassium hydroxide.