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127 Yale L. J. 2026 (2017-2018)
Horizontal Shareholding and Antitrust Policy

handle is hein.journals/ylr127 and id is 2103 raw text is: FIONA SCOTT MORTON & HERBERT HOVENKAMP
Horizontal Shareholding and Antitrust Policy
ABSTRACT. Horizontal shareholding occurs when one or more equity funds own shares of
competitors operating in a concentrated product market. For example, the four largest mutual
fund companies might be large shareholders of all the major United States air carriers. A growing
body of empirical literature concludes that under these conditions market prices are higher than
they would otherwise be. We consider how the antitrust laws might be applied to this practice,
identifying a theory of harm and how it matches the law, examining the issues that courts are likely
to encounter, and attempting to anticipate litigation problems. While the current literature on hor-
izontal shareholding does not offer a single robust explanation of how the price increase mecha-
nism works, we show that the effects test expressed in the Clayton Act does not require proof of
the precise mechanism. Further, Section 7's solely for investment exception typically will not
apply. We also briefly discuss special problems of private plaintiff challenges. Finally, we elaborate
the two ways that efficiencies are relevant to analysis of such mergers.
A U T H O R S. Fiona Scott Morton is the Theodore Nierenberg Professor of Economics, Yale
School of Management. Herbert Hovenkamp is the James G. Dinan University Professor, Univer-
sity of Pennsylvania Law School and Wharton School, University of Pennsylvania.

2026

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