We investigate the success of legislation aimed at increasing competition at highly concentrated U.S. airports, mainly by forcing these airports to increase the availability of scarce facilities. We use a multidimensional regression-discontinuity approach to exploit a sharp discontinuity in the law’s implementation and identify its effects. We find that fares decrease by 13.4% (20.2%) in markets with one (both) end point(s) covered. Approximately half of the decline is driven by the entry of low-cost carriers. We find little evidence that the fare declines were accompanied by a diminished quality of service, and passenger volumes increased, which suggests the legislation improved consumer welfare.