For sometimes now, I have known the official criteria for waitlist orders are:

1.Status
2. Fare paid
3. Time added to DM list

This is true in the US airport from my personal experience.

I have also posted the following experience in another thread:

I requested for C upgrade 3 days before my HKG-ORD flight, and was told there were 10 other 1Ks on the C upgrade list. On the date of travel, I got to the airport late, and was told no one has clear the waitlist. There were 36 1Ks on the waitlist at the time I checked in. I asked the agent what were the criteria in selecting which 1K get to sit in C in case seats became available. Agent told me: "the 1K who joined MP the earliest will get the nod".

At the gate, I was the fortunate 1K who got the C upgrade out of the 36 1Ks on the list.
I checked with the gate agent about the criteria, and was told I was selected because I was in MP longer than others.


Before that particular flight, I had only accumulated less than 10,000 YTD miles. I paid Q fare on that flight, and I was the 11th 1K to add on to the waitlist. I joined MP in 1991.

Obviously, UA-HKG seems to follow a different set of rules! Anyone has similar experience at UA's international locations?