It's called biodiesel. There's lots on the internet about it. Many restaurants will give you the old oil for free just to take it off their hands. By adding rubbing alchohol (I think) in just a few hours you can have diesel fuel usable in any tank that has been slightly modified.

But what I haven't been able to find out is if it only works if you currently hae a diesel engine...or can any car use it.

Anybody know anything about this?