Is GPM superior to MPG? Reuters article published in The Washington Times 2008 June 27 issue discusses the differences between MPG & GPM [km/L & L/km].
In short, it depends on what your objective is. GPM [L/100 km] is better for determining total costs of a vehicle operation say over a year, while MPG [km/L] is better for a more immediate operation like How Far Can I Travel on the Number of Gallons [L] I have in the tank to get to the next destination such as a refueling station. I opt for km/L (mpg) since that's my most immediate requirement while driving every day. Since I know by the fuel gage how many gallons [L] I have in the tank, it's intuitive or a single computation needed to make a decision. Conversely, if I want compare vehicles to know the total quantity of fuel needed to travel 10,000 miles in a year and the cost difference between different vehicles being considered, then GPM [L/100 km] is better. However, that is a one time computation during a purchase whereas gallons [L] are known by the fuel gage in vehicles and are used daily. Mental adjustments still are needed to adjust to the type of driving and weather/climatology conditions. Stan Doore
