If you go strictly by the EPA ratings, the 2012 Mazda Mazda6 doesn't have gas mileage that's especially noteworthy—or even close to class-leading.
Its EPA ratings, of 18 to 22 mpg city and 27 to 31 highway are merely average, or a bit below average, among mid-size sedans. But based on our real-world results, we think these ratings might be slightly pessimistic in this case; we've seen toward the high end of EPA Combined figures with the four-cylinder and the V-6.
Nevertheless, you won't see anything close to the Hyundai Sonata's 35-mpg highway rating in the Mazda6. Strictly by the numbers, there are plenty of greener options.