Every American knows what “fuel mileage” is—especially these days. Whether it’s the EPA test results on the window sticker, or the actual mileage you figured out for your car, we’re all asking: How many miles can we go on a gallon of fuel? In Europe and Asia though, fuel efficiency is measured by how many liters of gas it takes to go 100 kilometers. So what's the difference? A new study released by Duke University’s Fuqua School of Business sheds some light on why "miles per gallon" is inferior to "fuel consumption."