The Subaru WRX can't match the peerless gas-mileage numbers its all-wheel-drive Impreza sibling can--but for such a high-performance machine, it's in the above-average range.
With the manual transmission, the WRX earns a rating of 21 miles per gallon, 28 mpg highway, or 24 mpg combined. Subaru has a good track record of certifying fuel economy correctly, and those figures are exactly as the company predicted
With the CVT, the WRX is rated at 19/25/21 mpg. Subaru says if you left the CVT in Intelligent mode all the time you'd edge closer to 24 mpg combined, but the sport sedan probably will live in Sport Sharp mode most of the time, negating the gains from the CVT itself.
The WRX STI is rated at 17/23 mpg, or 19 mpg combined.
For comparison, the CVT-equipped Impreza sedan and hatchback get 27 mpg city, 36 mpg highway, for a combined 30-mpg rating. Manual numbers are somewhat lower, at 25/34 mpg.