Fuel consumption makes more math sense, especially when doing mental math comoarisons. Litres per 100km or the newer Gallons per 100miles for USA makes it easier for linear fuel consumption calculations. This quote explains: "The advantage of measuring fuel consumption this way is that it makes comparisons easier as fuel efficiency improves for a specific vehicle. That’s because the differences are linear. With miles per gallon, efficiency is graded on a curve. For example, for a 15-mpg car, a 5-mpg improvement is a 33-percent gain. But that same 5-mpg upgrade for a 30-mpg car is only a 17.5-percent improvement to a vehicle that is already using half as much gas. " With litres per 100km a 5 litre increase is 5 litres regardless of starting fuel consumption.