Biodiesel is an alternative fuel made by transesterification of fatty acids. The most commonly used feed stock today is corn oil, an unsustainable resource (the use of corn to make biodiesel and ethanol has had terrible consequences for common people in Mexico, for whom corn tortillas are economically equivalent to our "loaf of bread") but it can as easily be made from algae. Biodiesel is also commonly made from waste vegetable oil (from restaurants et cetera) and can even be made from animal fats, although the process is more complicated.