I own a VW New Beetle. It is a diesel engined vehicle that gets 45 to 50+ miles per gallon of fuel.
It will also run on bio-diesel fuel which can be made from vegetable oils (used or new).
About 3 years ago, I made bio-diesel - for about .50/galllon and ran my previous VW Rabbit diesel on it all summer long.
Perhaps I need to gather the items together to start making bio-diesel again.
Regards,
Jim TX