Originally Posted by
RSSRNotInIndia
There is a science to this ; ).
Paid gate (and easy/united.com) upgrades are offered only to those passengers who have purchased certain fare classes. Further, a specific dollar amount is assigned based on flight length (3000-4000, 4000-5000 miles, etc.) I don't work at the airport, but I have access to the profile, maybe one day I'll post the contents here. : )
The only rule I have ever seen enforced is no upgrades from NC-- and not all stations/CSR's seem to enforce it.
My understanding is that UFC's, when offered, are valid on most tickets that book into C/D/Z/Y/B/E/M/U/H/Q/V/W/S/T/XC/XY/NY. I don't know if they are good on K/L or opaque fares-- I believe they are not good on tickets with ID designators, and G fares.