Biodiesel is a fuel grade non petroleum based fuel source that can be used in any vehicle with a diesel engine. It's made from vegetable oils such as corn or soybean oil and it is put through a process to have the glycerin extracted from the oils.

One area where people get confused when talking about Biodiesel is understanding the difference between "Biodiesel" and raw vegetable oil. Biodiesel is the fuel grade derivative of raw vegetable oil. Any diesel engine can run biodiesl fuel, usually without any kind of changes being done to the car or truck. So essentially, biodiesel works exactly like gasoline works. You pull up to the pump and fill up.

A lot of commercially sold biodiesel is mixed with petroleum based fuels, but 100% biodiesel fuel can be used as well.

As I noted above, biodiesel isn't raw (or straight) vegetable oil, but straight vegetable oil, or SVO, as it is frequently referred to, can usually be run in a diesel engine as well -- after some modifications are made.

When alternative fuel aficionados are talking about biodiesel, frequently it is the use of straight vegetable oil or waste vegetable oil (WVO) that is being talked about. While svo is too viscous to run in your car unmodified, some changes can be made so that the oil's viscosity will be reduced before it reaches the injector.

If you're looking to save money on gas, doing an SVO conversion to run your diesel car on vegetable oil usually is going to make more sense than trying to find a gas station that has Biodiesel, mostly because you'll be hard pressed to actually find one and it won't prove to be actually cheaper than just filling up with regular diesel.

Cars that have been converted to use SVO or WVO are frequently referred to as Grease Cars. Some of the more popular cars to convert are older diesel Mercedes. Since straight vegetable oil is not approved as a fuel source, converting a new car to run one will more than likely void your warranty, so it is best to do the conversion on an older, reliable car and Mercedes definitely qualify, as do some Volkswagons, etc.