I don't know for sure, only what I saw. But they took an old diesel mercedes and disconnected the fuel line to the fuel injection and replaced it with a canister filled with filtered used cooking oil (maining it in to the fuel injection or throttle body??) And drove it around. My father just sent me a video today of a company that is making prototypes for the military's HumV that runs on gas or WATER, The guy invented a welder that runs on water, I guess it turns it into hydrogen gas. I'll try to get a link here.
Here is the site http://hytechapps.com