We’ve all taken econ 101 and know the basic laws of supply and demand. The airlines are not immune to to these rules; they just have greater power to flex them. In finding and booking your ideal ticket, your job is to figure out where demand meets your schedule and to book far enough in advance before the price goes through the roof. But before you can find the cheapest fare, you first need to understand how each seat is priced.
In an earlier discussion about fare buckets, I explained the basics of how fares are coded among classes and prices on an any given plane. While these are different for every airline, most legacy carriers have them grouped into blocks of First, Business, Coach and Award. Among each tier are stratified layers of fares, each with different rules, perks and prices. For 90% of travelers who are only concerned about cost, however, most of that chaff is irrelevant.
Ordinarily, unless one is looking for a particular fare or route, the least expensive fare out of a tier will be sold first. It’s what pops up first in a “search by price” query. As an example, if I’m booking a flight between Detroit and Chicago right now, the deepest discount I can get is on a K fare on Northwest for 49$ one way. If those sell out (and I still want an economy ticket), something in V or T will pop up for 79$ OW.