Competitive Harm from Vertical Mergers

35 Pages Posted: 24 Sep 2020 Last revised: 3 Sep 2021

See all articles by Herbert Hovenkamp

Herbert Hovenkamp

University of Pennsylvania Carey Law School; University of Pennsylvania - The Wharton School

Date Written: October 24, 2020


The 2020 Vertical Merger Guidelines produced by the antitrust enforcement agencies introduce a nontechnical application of bargaining theory into the assessment of competitive effects from vertical acquisitions. The economics of such bargaining is complex and can produce skepticism among judges, who might regard its mathematics as overly technical, its game theory as excessively theoretical or speculative, or its assumptions as unrealistic. However, we have been there before. The introduction of concentration indexes in the Merger Guidelines was initially met with skepticism but gradually they were accepted as judges became more comfortable with them. The same thing very largely happened again when unilateral effects theories of mergers were introduced in the 1990s. The bargaining theory that drives much of vertical merger analysis today has much in common with the theory of unilateral effects. In any event, the value of a particular model depends not on its verisimilitude but rather on its testability.

The theory that relates a concentration index to the risk of competitive harm from horizontal mergers involves as much conjecture as does the bargaining theory that the Nash model for vertical mergers contemplates. The concentration thresholds in the Horizontal Merger Guidelines capture a rough generalization about a large number of collusive or oligopolistic strategies, some of which are not consistent with each other. What they share in common is belief in a link between the number of firms in a market, the increase in concentration that results from the merger, and the extent of higher prices.

Double marginalization as a vertical merger defense occurs when two bargaining firms each have market power but are unable to coordinate their output. Each takes a markup without considering the other, and aggregate markups are too high. Both firms as well as their purchasers would be better off if they could coordinate better. In the AT&T/Time-Warner case the defendants argued that after the merger TW would not coordinate with AT&T but would set its prices as if the merger had not occurred. In that case the merger would not have eliminated double marginalization either.

The debate over the elimination of double marginalization bundles two themes that Ronald Coase developed in his two most well-known articles, The Nature of the Firm and The Problem of Social Cost. The first argued that the boundaries of a firm are determined by the firm’s continuous search to procure inputs in the most cost effective way. The second argued that two traders in a well-functioning market will achieve the joint-maximizing solution.

This dual relationship is too often ignored. Anti-interventionists rely heavily on Coasean arguments that unless high transaction costs get in the way firms will bargain to joint maximizing results. If that is true, then double marginalization will rarely provide a defense to a vertical merger. The law of vertical mergers deals largely with firms that transact with one another routinely, in legally enforceable buy-sell relationships. By contrast, the actors who appear in The Problem of Social Cost do not bargain with each other regularly. In a well functioning vertical market durable double marginalization should be rare.

Keywords: antitrust, mergers, verticalmergers, Nash bargaining, efficiencies, Coase, Organization, Competition

Suggested Citation

Hovenkamp, Herbert, Competitive Harm from Vertical Mergers (October 24, 2020). U of Penn, Inst for Law & Econ Research Paper No. 20-51, Available at SSRN: or

Herbert Hovenkamp (Contact Author)

University of Pennsylvania Carey Law School ( email )

3501 Sansom Street
Philadelphia, PA 19104
United States
319-512-9579 (Phone)

University of Pennsylvania - The Wharton School ( email )

3641 Locust Walk
Philadelphia, PA 19104-6365
United States

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