Based on the more recent
Upgrade benefits in the 2012 MileagePlus program (and this matches what was posted on the preview site before it was shutdown)
On these flights, our upgrade hierarchy will be:
•Global Services (all upgrade types)
•Instant upgrades that weren't confirmed in advance, on select Economy tickets, sorted by fare class, then status
•Global Premier Upgrades, Regional Premier Upgrades, and Mileage Upgrade Awards, sorted by status, fare class and date of waitlist
•All remaining Premier members, by status, then fare class
All GS (on any fare -- but GS tend to be full fare) are ahead of everyone