For a large all-wheel-drive car with supercharged V-6 performance, the 2013 Audi A7 lineup earns fairly good gas mileage. Its 18 mpg city, 28 highway EPA ratings are better than some other all-wheel-drive sedans that are smaller and lighter.
We can give credit to the 8-speed transmission for part of that. The gearbox has a wide range of gears, including a tall top gear for long highway jaunts.
From what we've seen, the A7 is fairly green in the real world, too, if you show some restraint. Over about 120 miles of driving in mixed, mostly relaxed driving conditions, we saw an average of nearly 22 miles per gallon. But we noticed that as soon as we dipped into the supercharged engine's reserves, our averages dropped noticeably.
The high-performance S7, with its 420-horsepower turbocharged V-8, is actually nearly as efficient. It has 17/27-mpg ratings. It's worth pointing out that the A7 manages just 1 mpg better overall than the larger A8 L sedan, which has a considerably roomier interior and much more backseat space.
If you're OK with a model that's much more conservative in appearance and feel, the Mercedes-Benz E350 Bluetec gets an EPA-rated 33 mpg highway.