I've been wondering this for a long time and Google doesn't seem to want to give me the answer.
In the United States, the term "miles per gallon" is most commonly used to express the fuel efficiency of an automobile. Given that "mile" and "gallon" are artifacts of the U.S. customary system of measurement, how would someone in a country that uses the Metric system go about expressing this rate? "Kilometers per liter"? "Meters per U.K. gallon"? "Furlongs per hogshead"?