A diesel engine will go much farther on a gallon of fuel that the standard gasoline engine because of their designs, and due to the higher energy density of a gallon of diesel fuel. But, it also takes a bit more oil to manufacture a gallon of diesel than a gallon of gas, with the production and refining processes for diesel producing more gases that trap heat.

Therefore, when you consider the relative merits of deisel and gas cars, try knocking the MPG estimates for the diesel car down by 20 percent. A diesel vehicle will cost you a bit more, so you’ll get more bang for your buck from a gasoline vehicle.