Agree w/AJC: trying to pin this down to a few simple and absolute rules is a waste of time. I'm not a corporate anything, and the first year I was invited (3 years ago) I had less than $20K of high yield and maybe $30K overall. Small market, so I suspect that's a factor...but really, you either get an invite the first time, or you don't. And there's no reason for United to divulge the "exact" basis for their invitations. All we really know is that if you fly a lot of high yield fares, especially from secondary markets, and your odds go up. Oh, and it's probably easier to requalify than to get the original invitation.