The best the SLS AMG GT can do is 13 mpg city, 19 mpg highway, and 15 mpg combined, per the EPA. That score applies to both the Coupe and Roadster models of the car.
The SLS AMG Black Series kicks up the horsepower and knocks down the gas mileage to 13 mpg city, 17 mpg highway, and 14 mpg combined.
For those truly desiring the best of both worlds, however, there is the extremely limited-edition SLS AMG Electric Drive, an all-electric version of the car with similarly stunning performance. Unfortunately, it's not available in the U.S. yet, so you'll have to arrange your own gray-market import.