Will BFGoodrich All-Terrain A/T KO tires kill my gas mileage?

I have a dodge dakota and need to put tires on it. I really like the bfgoodrich all terrain and have read excellent reviews on them, but with gas prices going the way they're going, should I put these tires on or stick with the goodyear wranglers that came from the factory, which i haven't had any problems with anyway?