They key difference being, as a 75K/100K, show me the cheapest "eligible" fare for immediate upgrade. In this particular example, there isn't any upgrade space for immediate upgrade, so you would be placed on the upgrade waitlist.

The relevant distinction is that "eligible" fares for your tier are added immediately to the upgrade waitlist, not the upgrade "request" queue for your Elite Tier like they would be for "ineligible" fares classes. As we know, at the Elite Tier windows, those in the "request" queue are moved to the upgrade waitlist, first by Elite Tier status, fare class, MM status and time in the queue.

With "eligible" fares, you are added directly to the upgrade waitlist in FIFO (first-in-first-out) order regardless of Elite Tier status. An MVP buying a B class ticket would be ahead of an MVPG100K purchasing an M class ticket subsequently.

Should U space open between purchasing an "eligible" fare and the 75K/100K window opening at T-120 and the upgrade processor actually fires, the upgrade(s) should process those already on the upgrade waitlist.

However, if U space never opens before the 75K/100K upgrade window at T-120 hours, the upgrade waitlist is reshuffled as 75K/100K Elites in the "request" queue are moved to the upgrade waitlist. Purchasing an "eligible" fare prior would give higher upgrade positioning (fare class) but the lower Tier "eligible" fare purchase is now out of luck.

With all the upgrade processor issues, I would never recommend purchasing an eligible fare unless you can confirm the upgrade at booking.

I never purchase eligible fares when I am traveling on my own. If I am traveling with my companion, I will use a Companion Certificate on GGU eligible fares only if there U space available. The fare differential is lower and you only pay it once.

James