They added the first bump in the playing field when most of them went to some degree of "a la carte" pricing for their lowest fares. They unbundled their total fare into a base plus fees for extra features. But, in many cases, different lines unbundled different elements of the service. Some lines added the next bump by re-bundling service element combinations into different fare levels. The lowest level got nothing beyond a seat on a plane, but the next level up might include a checked bag, earlier boarding or a lower change fee. Only a few OTAs and search engines have the ability to post those individual fare levels. More recently, Delta announced it would remove its fare displays completely from some big OTAs. This move may be permanent, with Delta's joining Southwest in limiting fare information to third parties. But it could also be a ploy to negotiate lower payments to the several third parties in the online process. Get the full story at the Chicago Tribune