Losses from Horizontal Merger: The Effects of an Exogenous Change in Industry Structure on Cournot-Nash Equilibrium

The consequences of a horizontal merger are typically studied by treating the merger as an exogenous change in market structure that displaces the initial Cournot equilibrium. In the new equilibrium the merged firm is assumed to behave like a multiplant Cournot player engaged in a noncooperative game against other sellers. The purpose of this article is to evaluate an unnoticed comparative-static implication of this approach: some exogenous mergers may reduce the endogenous joint profits of the firms that are assumed to collude. Cournot's original example is used to illustrate this and other bizarre results that can occur in the Cournot framework if the market structure is treated as exogenous.