The 2013 Toyota FJ Cruiser is only offered with a rather thirsty 4.0-liter V-6 engine; but mileage does vary depending on whether you choose rear-wheel drive or four-wheel drive, stick or automatic.
With rear-wheel drive and the five-speed auto, you get 17/22 mpg city/highway and 19 mpg combined. Four-wheel drive lowers that estimate by only 1 mpg. And it would be sacrilege to get an FJ without four-wheel drive.
The automatic transmission is really the more fuel efficient option here. Go with the manual, and mileage drops to 15/20 mpg city/highway and a combined figure of 17 mpg.
Compared to other mainstream SUVs, those are some very low numbers. But they are closer to what other sturdy off-road models like the Nissan Xterra or Jeep Wrangler return.