The deisel engine was invented to run on cotton oil! it will actually run on any liquid oil - hemp, sunflower, old rancid chip-shop oil, etc. thus if we could all grow our own dope, we could run our cars, eat high protein cakes, get the correct ratio of omega 6's to 9's, wear cool clothes and be perteually high. man that'd be heaven!
A lot of newer cars are what they call dual fuel vehicles. They will run on gas or e85 which is 85% ethanol. The Biodeisel which is made from vegetable oil is not as simple as using used oil. It needs to be refined but it is not that difficult.
The Show Dirty Jobs featured this one night. He used the oil from deep fryers. Pretty cool stuff.
vegetable oil is great and we have the ability to produce a virtually unlimited supply of it. I know in our area there is alot of farm land that is being paid to not be planted.