The great thing about biodiesel is that no conversion of the diesel engine is necessary. Just convert to a station that sells biodiesel and fill er up.

Most modern diesel automobiles can already be used with biodiesel - but only to a point. Biodiesel is chemically different from conventional diesel fuels and, among other factors, has a higher solvent action. This can lead to premature failure of components in the fuel system, for example. Low ratio blends, such as B2 and B5 (2% and 5% biodiesel, respectively) rarely cause problems, but higher blends can damage some vehicles. B20, 20% biodiesel, is a common commercial blend and is not recommended for use with many vehicles. B100 or neat biodiesel is even more problematic. There is little the consumer can do about these issues. An engine cannot be easily converted to biodiesel, for example, by purchasing a couple of new parts for the fuel injection system off the shelf. You need to check if you vehicle is compatible with biodiesel, from either the manufacturer or from the Engine Manufacturers Association (http://www.enginemanufacturers.org/). The use of biodiesel in your vehicle may void the warranty. The following is taken from the EMA's "Technical Statement on the Use of Biodiesel Fuel in Compression Ignition Engines": "Neat biodiesel and higher percentage biodiesel blends can cause a variety of engine performance problems, including filter plugging, injector coking, piston ring sticking and breaking, elastomer seal swelling and hardening/cracking, and severe engine lubricant degradation. ... In addition, elastomer compatibility with biodiesel remains unclear; therefore, when biodiesel fuels are used, the condition of seals, hoses, gaskets, and wire coatings should be monitored regularly."

This question has already been answered by John, but I thought I would share some useful resources on this topic. One of these links describes how to make your own biodiesel fuel too. http://www.ravenfamily.org/andyg/vegoil.htm http://journeytoforever.org/biodiesel_make.html