It's nearly impossible to tell if a flight will require volunteers (or IDB's for that matter) right up until departure time. To get a good picture you need both the actual number of seats booked AND the availabe inventory (the ones that show all the numbers). The inventory in and of itself is only good enough at both extremes (either wide open -- all 9's -- or overbooked, which is all zeros and referred to as "zeroed out"). I've gotten on flights (as an SA) that are overbooked by 20 or 30 and I think there were still seats available to be sold. If it's overbooked by 15 and they're still selling seats, odds are they won't be taking volunteers. If it's overbooked by 5 and they're not selling any more seats, you can still figure on a couple of no shows and a couple of misconnects. The system UA uses for nonrevving is completely automated and tells you open seats up to 25 (i.e., it will say the specific number of seats until it gets to 25 at which point it says "more than 25 seats open") and oversold seats up to 10 for every class of service. On mainline flights, it's pretty easy to tell whether or not you'll make the flight based on the availability and number of people listed. It falls to pieces when it comes to express flights because you just never know when they'll take a weight restriction. Overbooking/bumping is really market specific, such that some flights will always be taking VDB's where others that are overbooked aren't and rarely do.

Edited to add: In response to the comment about leaving the poor agents alone, call late at night during off peak times. Calling during the day when there are "lines" means that everytime somebody calls about a trivial question, they're making somebody who has a substantive transaction to complete wait on hold. With the closing of a bunch of res centers, I think it's pretty obvious that hold times will go up.

[This message has been edited by DHAST (edited 11-11-2002).]