Originally Posted by WalruSara

There is also the possibility of being offered an upgrade for purchase at the kiosk. However, this is always left up to chance -- the availability of seats, the class of ticket purchased, etc.

I was offered the upgrade from JFK-LHR in May for $770. No upgrade available for my DFW flight, but the upgrade was offered when I stopped by the airport the morning of departure.

Worth every penny. :-P