Whether it's mental, written on an envelope or meticulously documented in a spreadsheet, a list of pros and cons often plays a role in the purchase of a new car.
What's the mileage like? How safe is it? How's it look?
If a shopper was weighing whether or not to buy a natural gas-fueled car, the top item on the "pro" side would without a doubt be the cost of fuel: right now the gallon-equivalent of compressed natural gas costs less than half as much as a gallon of gasoline.