In
antitrust economics, common ownership describes a situation in which large
investors own
shares in several firms that compete within the same
industry. As a result of this overlapping ownership, these firms may have reduced incentives to compete against each other because they internalize the profit-reducing effect that their competitive actions have on each other. The theory was first developed by
Julio Rotemberg in 1984. Several empirical contributions document the growing importance of common ownership and provide evidence to support the theory. Because of concern about these anticompetitive effects, common ownership has "stimulated a major rethinking of antitrust enforcement". Several government departments and intergovernmental organizations, such as the
United States Department of Justice, the
Federal Trade Commission, the
European Commission, and the
OECD, have acknowledged concerns about the effects of common ownership on lessening product
market competition. Asset managers have disclosed these concerns as regulatory risks, with
BlackRock stating in its 2023 annual report that the common ownership theory "purports to link aggregated equity positions in certain industries with higher consumer prices and executive compensation and lower wages and employment rates." In May 2025, the
Federal Trade Commission and
Department of Justice filed a statement of interest in
Texas v. BlackRock, State Street, and Vanguard, asserting that institutional investors may face liability under Section 7 of the
Clayton Act for using shareholdings in competing firms to restrict competition. == Contract theory ==