Squeezing Gas from a Cow. I saw this in Popular Mechanics, kind of awkward really...(especially for you of the vegan persuasion) but hey, Iʻm all for new ideas in making the world run greener.

"Next time you hail a cab in Sweden, there might be beef in your rideʻs tank. The city of Linkoping is running one train, 67 buses and 80 cabs entirely on biogas, a methane fuel made primarily from cow intestines and other slaughterhouse waste."