Usually derived from vegetable oils-soy is very popular these days, but animal fats can also be used-biodiesel is made through a chemical process called transesterification which essentially splits the oil into two parts: alkyl esters and glycerine; the esters are the fuel, while the leftover glycerine is often used to make soap and other beauty products. Both virgin and waste oil (often collected from restaurants) can be used in this process with equally good results.

A common misconception is that engine modification is needed to use biodiesel. This is simply not true: any diesel engine can burn biodiesel without any modification; it's a straight fill-up-and-go affair. Unfortunately, it isn't available at every gas station and truck stop in America just yet, but there's something you can do about that: make your own.Courtesy of Willie Nelson, country singer and biodiesel booster extraordinaire, this recipe is featured in Willie's new book, On the Clean Road Again: Biodiesel and the Future of the Family Farm.

Caution: Making your own biodiesel can be a dangerous process; please, be extremely careful and wear safety glasses or goggles, a face mask and heavy-duty gloves.