I regularly get about 15 mpg.
I do a fair amount of 80mph highway driving. Without that, 13 would not surprise me. It is a very heavy vehicle. Wish they had made a bigger gas tank. I'd rather get 12 mpg but get 350 miles between stops versus 15 mpg but have to stop 100 miles earlier.
I never mind the fill ups however. The X5M is a pleasure to drive and super practical.