US Big Four capacity growth has pushed the natural oligopoly rules

The US domestic airline market is getting tougher for new entrants as the Big Four grow ever larger. In defining the Big Four we combined appropriate pre-merger fleets for the period to allow for a fair comparison. The growth for two of the Big Four spikes in an interesting way. It appears the oligopoly is currently out of balance and the question is how long can this go on?  Also, a secondary question – how hard is it for a new entrant (like Moxy) in this market?

Starting with national domestic market share, note the Big Four are getting bigger.  The top part of each column is “Other” and it shrank to a steady 7%.  Recent startups like JetBlue have stayed with the same market share.  Alaska grew its market share by buying Virgin America. Even Southwest bought market share via AirTran.