Depends on a lot of factors : CVT (better), M6 (not so good), 4AT (worst), wheel size, correct air pressure in tires, type of gas, ethanol or not, temperature. Then there is driving : highway, city, gradual vs fast accelerations and decelerations, stable or constant variation (even slightly) on gas pedal, speed, weight carried, etc. Mine (LE Eco base) never fail to give me between 30-50 (39 average, calculated over 2½ years). I'm not hyper milling, but I would certainly qualify for "easy driving" though.