Yeah, that may be something to try. The wow factor is that we take used fryer oil, treat it with some chemicals, and end up with a fuel and glycerine (which can be used in soap, cosmetics, candles). I may try straight veg. oil sometime.

About the question, what makes something biodiesel... Biodiesel is the term for fuel derived from renewable sources like vegetable oil. The most common procedure is to split the normal triglyceride into smaller molecules -- this makes it a drop-in replacement for dino diesel. Some people run straight vegetable oil, but this is less common because it's difficult to atomize the fuel and it clogs the injectors.