There has been discussions going on in Europe about people filling there car up with what we call lettuceoil. It is oil you would mix a salade with. It is not olive oil!
It is really cheap, 60ct for a liter while diesel here is now at record heights of about 1,05 euro for a liter. I have a common rail diesel, so it is important that the mixture stays very fluid. So I mix it on a 80% diesel and 20% lettuce oil. On a 60 liter tank, that will save me about 5 euro's per tank!
Maybe something to explore for others? The only downside I can find is that your exhaust smels like fries ;-)