US has Space Available (SA) and Space Positive (SP) upgrades for transatlantic flights, however, I have not seen any system wide upgrades like those issued by UA. If I recall correctly, the SA upgrades cannot be confirmed before booking, and, unless you have status, you generally cannot request an upgrade until two hours before a flight -- the SA can be used on most purchased tickets (though I have heard of some rare refusals for use with the really cheap internet fares). As for the SP upgrades, they can be confirmed prior to the flight, but can only be used on a limited number of fares. You may be able to get greater detail in the US forum.