If I weigh 314 lbs will I fit in a southwest airlines seat?

I thought about going american airlines, but I just need to be able to fit, i'm a tidbit worried about that. Anyone else who's larger have experiences with southwest, or american airlines with seating? Last time I flew was in 2006 we flew to atlanta, but we flew delta, and I barely fit. I plan to try and loose some of the pounds, but I dont want to book a flight and then not fit.