The six network carriers in the US (AA/ UA/ DL/ NW/ CO/ US) function as a cartel, but aren't one on paper (except at Orbitz). They adopted the cartel economic strategy around 1992. Their terrible Gulf War-era financial losses convinced them that it wasn't worth going after each others' market share with low fares. All that did was hurt everyone's yields. People Express was gone, the merger mania of the late '80s had settled out to six major carriers, and all six had high fixed costs.
So it made more sense to limit capacity, hike fares, and compete *only* for the high-fare business travelers with bigger and better clubs, and FF perks. Leisure folks were screwed, except in the fortunate cities that had Southwest. That's a cartel strategy, even if there was no on-paper collusion. There didn't need to be any. Common economic interest--unions and management/ shareholders had the same interest--dictated the "let's all agree to leave each other alone except on high-fare buisness pax" strategy. Which was *not* the interest of paying passengers.
The Department of Justice has alternately treated the Six Families as individual businesses, and as a cartel. DOJ rejected UA-US last year at least partially because it would have certainly led to industry consolidation.
Orbitz is most definitely a cartel creature--five of the Six families get together to distribute their lowest seat-dumping leisure fares at one site. Why DOJ hasn't shut down that anticompetitive beast, I don't know. It's *entirely*--read *entirely*--intended to destroy low-fare competition. What could better fit the dictionary definition of collusion, I don't know. The entire idea is to market the Cartel as a big source of low fares. Yeah, right. If Southwest weren't around we'd all pay through the nose, and Orbitz would mysteriously evaporate.
Need a new airline paint scheme? Better call Saul! (Bass that is)