The Role Of Market Definition in Assessing Anticompetitive Harm in Ohio v. American Express

This article shows that the Supreme Court reached the right outcome in Ohio et al. v. American Express. The District Court had found that American Express was a two-sided transaction platform that provided joint services simultaneously to cardholders and merchants. But it then chose, by adopting a single-sided merchant services market, to analyze the effect of the anti-steering provisions at issue solely on one side of these simultaneous transactions. That decision appears to have prevented the lower court from seeing that the plaintiffs’ evidence of anticompetitive harm to merchants was wea…