Oliver Hart and Jean Tirole, April 1990
Few people would disagree with the proposition that horizontal mergers have the potential to restrict output and raise consumer prices. In contrast, there is much less agreement about the anti-competitive effects of vertical mergers. The purpose of this paper is to develop a theoretical model showing how vertical integration changes the nature of competition in upstream and downstream markets and identifying conditions under which market foreclosure will be a consequence or even a purpose of such integration. In contrast to much of the literature, we do not restrict upstream and downstream firms to particular contractual arrangements, but instead allow firms to choose from a full set of contractual arrangements both when integrated and when not. We also allow non-integrated firms to respond optimally to the integration decisions of other firms, either by remaining nonintegrated, exiting the industry or integrating too (i.e. bandwagoning). In a final section we use our analysis to shed some light on a number of prominent vertical merger cases, involving computer reservation systems for airlines, the cement industry and the St. Louis Terminal Railroad.