It gets credit for the efficiency wrought by a turbodiesel six-cylinder engine, but the 2011 Mercedes-Benz GL-Class scores poorly overall in our green rating because of its less efficient gas engines.
The least expensive GL--and frankly, our favorite--is the GL350 BlueTEC. It's a turbodiesel that uses an aftertreatment for its emissions, so that it meets tough diesel particulate rules in all 50 states. With an automatic transmission and four-wheel drive, the diesel six earns an EPA rating of 17/21 mpg, good numbers for a vehicle nearly the size of a Chevrolet Tahoe (and just about exactly the size of a diesel-less Dodge Durango).
From the diesel's peak, fuel economy across the GL-Class lineup drops sharply. With the 3.5-liter V-6 aboard, the GL450 checks in at 13/18 mpg. Tap the power of the GL550's 382-horsepower V-8, and fuel economy falls to 12/17 mpg--right down there with the least efficient Escalades and Range Rovers.