Mileage can vary depending on whether you choose a manual or automatic transmission, or rear- or four-wheel drive, but the FJ's 4.0-liter V-6 is pretty thirsty no matter how you slice it.
The rear-wheel-drive model with the automatic transmission is the most efficient version of the FJ, rated at 17 mpg city, 22-highway. We think choosing it without four-wheel drive is near blasphemy, though, and that system only lowers the fuel economy by 1 mpg.
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.