It's not going to bowl over efficiency aficionados, but the 2011 BMW X5 is actually one of the more efficient large SUVs available. The X5 xDrive35i, powered by a direct-injection turbocharged inline six-cylinder scores 16 mpg city and 23 mpg highway--as good as many mid-size sedans. The V-8-powered xDrive50i scores a less-impressive 14/20 mpg, but even that still manages to beat much of the similarly-powerful competition.
A diesel is available in the X5 xDrive35d, greening things up at 19/26 mpg, for 22 mpg combined, a commendable figure for a full-sized SUV that still has some sporting spunk.
The X5 M is all about performance, and the fuel economy figures reflect that: 12 mpg city, 17 mpg highway.