Fox

Well, you wouldn't want to buy food-grade veg oil to power a car anyway... most converted diesels can run on filtered waste vegetable oil depending on its consistency and amount of contamination.

They still need a little diesel to start up with though... the veg oil only works when the engine's heated up already. It can't be used to cold start.

I've heard about the air engine as well - it's compressed air if I remember correctly. Pretty neat concept, especially for short jaunts across town in a metropolis. And the real advantage would surely be the cost of maintenance, since an air engine should be relatively simple and not nearly as problematic as a combustion engine.