Here's how UAL Does it on Int'l Flights........

#1 Rule NO DOUBLE UPGRADES!!!! (example, no coach to first....only coach to busn class.....busn class to first class......no matter how many miles, status, fare paid.....not allowed they will go with open seats in first and buy people off before they double upgrade.....almost like a fire-able offense by a gate agent if he/she does it)....

They will upgrade business class customers based on ( 1) price paid for ticket, 2) actual mileage flown within the last 12mths) to first class.

Then they will upgrade coach customers based on the same criteria. Now 24-48 hours prior to departure is when they allow frequent fliers to log in and option to use their miles to upgrade.....so you'll usually see the loads change a bit in that time frame.......

Last they will fill all seats with standby's......FYI if you are not the employee, employee spouse/domestic partner, or a child (over 18)..........you are not elgilble for first class on any 3-class cabin international UAL flight unless one of the above is travelling with you.

Many times I've taken my mom on trips, and even though I'm working the trip, she is not elgibile for 1st class, cause I'm not writting a pass and travelling with her. Jumpseaters are "not" allowed first class on any 3-cabin international flight (if the f/a offers you the seat after you leave....that's a different story, but usually they won't, but will offer you business).