Don't assume you get equivalent energy from a "gallon" of propane compared with a gallon of gasoline or petrol. A gallon of propane contains 100,000 BTUs, a gallon of No. 2 heating oil (used in our homes here in New England) contains about 136,000 BTUs, and typically costs less than a gallon of propane (which has less "energy" in it). Don't know how many BTUs are in a gallon of gasoline, likely more than propane, though. There are conversion kits to make internal combustion engines run on propane, and you'd likely have to SERIOUSLY strap down propane tanks in your trunk to store the fuel. The earth will thank you, though, since propane generally has a cleaner emissions profile than gasoline and reduces engine maintenance requirements. What about biodiesel? I followed a 240 diesel home here near the quebec border. It was moving slowly and it smelled like a popcorn maker behind. Then I saw the biodiesel bumper sticker. chris in vermont, 244, 945, r100rs, etc.