• What are the chances that my upgrade will clear?

The answer is plain and simple: It varies! However, if you are using 500-mile electronic upgrades, priority is based on status, then other factors (see: How does the upgrade waitlist work?), so your chances are generally better if you avoid EXP-heavy routes on weekday mornings and evenings; these upgrades may clear any time from the beginning of your upgrade window (depending on status) to the time the gate agent closes the aircraft door. If you are using an award or systemwide upgrade, you can check for upgrade inventory availability prior to making your reservation to select a flight where you can request and clear your upgrade request immediately after your reservation goes from ‘Purchased’ to ‘Ticketed’; if upgrade inventory is not available, you will be waitlisted and these upgrades may clear anytime thereafter. Upgrade inventory cannot be viewed on AA.com, but availability can be determined by calling AA Reservations (+1 800-433-7300) to inquire. First Class upgrade inventory (A) can be viewed online with any public inventory tool, such as the KVS Availability Tool, a subscription service. Business Class upgrade inventory (C) is hidden from public inventory tools, but can be viewed using ExpertFlyer, a subscription service that also offers a free 5-day trial.

FlyerTalk member sica4 has also established a searchable database of 500-mile electronic / sticker upgrade request outcomes. All members are invited to search and to contribute here.

Wiki: Inventory Classes
FT: Understanding AA upgrade inventory on ExpertFlyer.com
FT: http://www.flyertalk.com/forum/ameri...solidated.html – [Contribute to sica4's sticker upgrade database.]