Considerations of Countervailing Power.

The 2010 Horizontal Merger Guidelines set forth the current antitrust enforcement practices but do not address mergers that result in bilateral monopoly. We show that, given the presence of lawful, enduring market power, such mergers may improve social welfare. As a result, these mergers deserve careful scrutiny before condemning them as anticompetitive. In this paper, we address this issue and suggest an economically sound enforcement policy. [ABSTRACT FROM AUTHOR]