Part of the issue, of course, is that the GLK only comes in GLK350 guise, with its comparatively large-displacement V-6. And it's quite heavy. Mercedes-Benz has suggested that it is considering adding a four-cylinder turbo-diesel model to the GLK lineup in a future model year, but no official announcements have yet been made.
The 2011 Mercedes-Benz GLK is really a compact—not mid-size crossover wagon—yet it has the fuel-economy ratings of a mid-size or larger ute. Whether you get the GLK350 with rear-wheel drive or the 4Matic all-wheel drive system, it's rated at a not-at-all-green 16 mpg city, and highway ratings are either 21 or 23.