Took a 2000+ mile trip to eastern Montana and consistently averaged 39mpg+ with many miles at three digit speeds in a E350 BlueTec. Fuel mileage is about the same in the GLK250. Both drop off to around 32mpg in local stop-and-go short mileage trips. Even with passengers and luggage the GLK250 was able to average right at 37mpg on more crowded European roads. The 250 is a winner!