I'd believe that gasolene engines could not be run on other less potent fuels if I didn't know about the gasgogen converters in use in France and perhaps England during WWII. These converters were large stoves that burned wood and the car ran off the methane and other hydrocarbons produced from the burning buring wood. They didn't go very fast or have a lot of power, but they sure beat walking around.

   This week Time magazine did a short bit on using pig manure and other things in some sort of a digestor to generate methane, and India has been using the manure of the sacred cattle walking around all over the country to generate methane for heating and cooking.

   Fuel oil itself can certainly be made from other ingredients, but it may not be a cost effective process, so it wouldn't work well in the long run.

Dave