The 2013 BMW 6-Series models offer several different powertrains that span a difference in power and capability.
Although there's no truly green choice, the turbo six-cylinder engine in the 640i variants is quite efficient, at 23 mpg city and 33 mpg highway in Coupe form, according to the EPA; the convertible scores 21 mpg city and 31 mpg highway.
Stepping up to the V-8 engine in the 650i, the hardtops get 15/23 mpg ratings with the eight-speed automatic, while the six-speed manual scores 15/22 mpg. Soft-top models score identical numbers.
There's also an xDrive all-wheel-drive version of the new 6-Series Coupe, which pays a penalty of just 2 mpg on the highway in comparison to rear-drive V-8 models, at 15/20 mpg.
The new M6 Coupe and Convertible are also impressive--on a relative scale. Compared to the previous V-10-powered M6, the new versions offer a 23-percent improvement in efficiency, according to BMW. But even with that improvement, they're at 14 mpg city, 20 highway (16 mpg Combined).