Gallons per mile
I also stand corrected.
I didn't know it shifted to bio, or at least I forgot. If you go to Neil's web page he has a short movie he made about a trip he took, the only thing I'm remembering about the movie now is that he drove past an ugly oil producing area, may have been tar sands oil.
stopped looking ages ago,,now its £40 to get to 1/4 of a tank in ours