Quote of the Day - I think if humans are really going to explore the solar system, or go beyond our immediate neighborhood, we are going to have to go with nuclear power. Nuclear power really is the development of the steam ship compared to sailing ships.
Imagine this: your car runs on leftover vegetable oil from your favorite neighborhood fast-food restaurant. The restaurant is happy because they don't have to pay someone to haul the used vegetable oil away. You're happy because you don't have to pay for regular fuel. Your car reports that the jury's still out because its piston valves are a bit sticky from time to time.
The Sierra Club is both happy and unhappy. On the one hand, you're not contributing carbon dioxide to the atmosphere and hastening the ice cap meltdown. On the other hand, however, you are contributing soot in the form of nitrogen oxides to the atmosphere (if there were a lot of you using vegetable oil, then it would be a very big problem). Not surprisingly, the petroleum industry is decidedly unhappy: they're not pumping high test into your car.
The USEPA is likewise unhappy, but they apparently don't care. Using vegetable oil to power your car is illegal, but the USEPA has bigger fish to fry (no pun intended), and frankly, they don't have the resources to hunt you down and slap you with a ticket.
So, you're off and running on vegetable oil.
But should you be? It may benefit one part of the environment, and hurt another, both at the same time. The monetary savings might be there, but there's a lot more work involved both with the conversion of diesel to vegetable oil, and then there's the decided lack of vegetable oil "gas" stations. You can use a restaurant, but unless you've planned ahead, you may run out of fries.
Then again, you could just go solar.