We analyze the efficiency defense in merger control. First, we show that the relationship between exogenous efficiency gains and social welfare can be non-monotone. Second, we consider both endogenous mergers and endogenous efficiencies and find that merger proposals are largely aligned with a...

We analyze horizontal mergers when the acquirer holds a passive partial ownership stake (PPO) in the target firm prior to the merger. We show that a PPO reduces the minimal synergy level necessary to make a merger beneficial for consumers. It follows that an antitrust authority ignoring existing...

This paper argues that it cannot be taken for granted that any merger that raises consumer surplus also increases social welfare. We assume a Cournot model with homogeneous goods, linear demand, and constant marginal costs, to show that a merger can raise consumer surplus while harming social...