What we need is an approach that distinguishes airfares that are high because of monopoly pricing from those on routes that are legitimately expensive to fly.
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The regression analysis also accounts for three other factors that have significant effects on pricing. These are, respectively, the market share at the origin and destination airports held collectively by the five “legacy carriers” (United, American, Delta, Continental and US Air); the market share held by Southwest Airlines; and the market share held by the largest single carrier at that airport (for instance, Delta and its affiliates are responsible for about 66 percent of all traffic at Atlanta).

¶Prices are higher the more the legacy airlines dominate an airport, but they also tend to be a bit higher where Southwest has a large share as opposed to other low-cost carriers like AirTran and JetBlue. (Southwest is cheap, but it isn’t quite as cheap as some of these up-and-coming airlines and now represents something of a middle ground.) Also, prices tend to be higher when any one airline dominates an airport, regardless of whether it is a legacy carrier or a low-cost one.