With their fuel economy ratings that range from 16 to 18 mpg in the city, and 23 to 26 on the highway, neither the V-6 M37 nor the V-8 M56 are all that frugal on gas.
All-wheel-drive models lose about 2 mpg, with the M56x at the bottom of the numbers, at 16/23—about the same as a large, three-row utility vehicle.
Gas mileage is 16/25 mpg with the V-8 and rear-wheel drive, 16/23 mpg for the V-8 AWD—decently improved figures for a car that weighs between 3858 and 4224 pounds.
What redeems the lineup somewhat is the M35h, an advanced hybrid sport sedan that achieves EPA ratings of 27 mpg city, 32 highway. And as we've found in a couple of extended drives, it performs nearly as well as the gasoline variants.
M37 and M56 models also get an "Eco Pedal" feature that gives haptic feedback when it senses the chance to save fuel.