Rick Larrick and Jack Soll of Duke University explain it all at The MPG Illusion
Which is more useful to know: How far you can drive on a gallon of gas? Or, how much gas you will use while owning a car?
MPG answers the first question. GPM answers the second question. We suspect that, when buying a car, most people want to know gas consumption. Gas consumption, as measured by GPM, can be directly translated to the cost of driving the car and to the amount of greenhouse gas emissions. MPG cannot.MPG can be a misleading measure of fuel economy when comparing two cars.