Im a gate agent and i know from what i am told, we can only do comp upgrades if we need the seats in the back, like full flights oversold etc, everything we do in the computer is linked to us, so if we comp and upgrade without permission from a sup trust me you are in the office with a union steward, being asked do you remember why you did this, and when we do comp upgrades we do it based on mp status, we do our globals first, one k's and premier execs etc, i will ask in breifing bout that, but i know from experience that is the only time they allow us to with out getting in trouble