Professor Emerita Valerie Suslow and Adjunct Professor Margaret Levenstein have pursued a collaborative research agenda on the economics of cooperative behavior among firms, with a specific focus on cartels. Agreements between competing firms to reduce the intensity of competition can include actions such as price fixing, allocating geographic markets, allocating customers, and bid-rigging at auctions. Historically, such cooperative behavior was legal throughout the world but illegal in the United States under the Sherman Act of 1890. 

The U.S. National Industrial Recovery Act of the early 1930s suspended price-fixing antitrust laws in certain circumstances. In the mid-1990s, after many decades of inattention, it became clear to competition policy enforcers that cartel activity was rampant and was likely causing substantial consumer harm. This spurred new leniency and amnesty policy tools to become available to firms. In their highly cited article "What Determines Cartel Success?" Levenstein and Suslow make the case that while cartels may break up due to cheating on the agreement, the more insurmountable problems are entry and adjustments in the face of changing economic conditions. "Breaking Up Is Hard to Do: Determinants of Cartel Duration" shows that cartels that turn to price wars to punish cheaters are not stable. Highly stable cartels draw upon a vast toolkit of mechanisms to enhance their stability and, therefore, their duration and economic harm. 

Levenstein and Suslow's work has been cited in policy reports by organizations around the world, such as the Organization for Economic Cooperation and Development, the United Nations, and the World Trade Organization. They continue to explore hidden or overlooked sources of harm to consumers that may result from cartel activity, most recently turning their attention to the role played by vertical relationships between firms engaged in horizontal collusion, as well as how collusion may be facilitated by the use of a price index in long-term contracts.