Endogenous horizontal mergers under cost uncertainty

This paper presents a study of endogenous horizontal mergers under cost uncertainty. Before knowing the exact values of their costs, firms decide sequentially whether or not to join a merger. After the merger decision is made, uncertainty is resolved and firms engage in Cournot competition with incomplete information about one another's costs. Due to production rationalization, the merged firms enjoy an advantage over non-merged firms in the sense that the merged firms' expected cost is lower. I show that mergers occur if and only if the uncertainty is large and that the larger the uncertainty, the greater the number of firms that will merge. Although a merger reduces competition and therefore hurts consumers, it improves productivity under cost uncertainty. I find that a merger increases social welfare whenever there are at least four firms in the industry before the merger.