The Determinants of State-Level Antitrust Activity* Robert M. Feinberg and Kara M. Reynolds Department of Economics American University August 2010 ABSTRACT While there has been a considerable literature exploring the determinants of antitrust enforcement in the United States, these studies have been based either on aggregate federal enforcement data over time (exploring cyclical influences) or cross-industry studies, usually for a single year or aggregated over several years. What has never been investigated is the pattern of state-level antitrust litigation. This is somewhat surprising, as this has been a major activity of many state attorneys general. In this paper, we explain state antitrust activity across states and time (for a 15-year period), examining a number of the economic and political determinants that have been proposed in the literature. Keywords: antitrust enforcement, political economy JEL Code: L44 *The authors acknowledge helpful comments from Joseph Clougherty, Robert Masson, Russell Pittman, David Round, Larry White, and two anonymous referees on an earlier draft. Of course, all errors and omissions are ours alone.