Originally Posted by dstan

• How do I book an upgradeable fare?

All published fares are eligible for 500-mile / sticker and EXP upgrades on AA flights within North America, the Caribbean, and Central America.

Fares booked in I, O, and Q (overseas) inventories are not eligible for award (miles + copay) or systemwide (SWU / eVIP) upgrades. Thus, the cheapest fare shown in the AA.com “Price and Schedule” booking engine may not be upgradeable, and the lowest priced upgradeable fare may not be offered as an option. The solution to this is to place a reservation at the cheapest fare on Hold, then to call AA Web Services (+1 800-222-2377) and ask the agent to increase the fare (‘upfare’) to the lowest upgrade-eligible fare. The purchase can often then be completed online without incurring a phone booking fee. In some cases, the AA website may revert to the lower fare when trying to complete the purchase, and in this case, one must call AA Web Services to complete the purchase over the phone; this can generally also be accomplished without incurring a phone booking fee if the agent understands that this is due to a system limitation. One drawback of the upfare method is that promotion codes can not be applied to Hold reservations, so one may have to choose between using the code or booking an upgradeable fare.

One can also search specifically for upgradeable fares on ITA, a powerful website that can be used to search for, but not book, simple and complex itineraries across one or more airlines. To restrict a search to exclude O and Q fares, add the modifier:

/f ~bc=o&~bc=q

After selecting an itinerary, click “Show booking details” to reveal detailed information on fare codes, taxes, and fees.

Wiki: Upgrades | Inventory Classes
FT: Upfaring an itinerary on Hold to an upgradeable fare class
FT: Upfaring and applying a discount / promotion code
FT: Mileage Run Discussion Forum: How to specify the booking code on ITA