Sharing systems are increasingly challenging sole ownership as the dominant means of obtaining product benefits, making up a market estimated at over $100 B annually in 2010. Consumer options include cell phone minute sharing plans, frequent flyer mile pools, bike sharing programs, and automobile sharing systems, among many others. However, marketing research has yet to provide a framework for understanding and managing these emergent systems. The present paper conceptualizes commercial sharing systems within a typology of shared goods. Three studies then demonstrate that beyond cost-related benefits of sharing, the perceived risk of scarcity related to sharing is a central determinant of its attractiveness. Results suggest that managers can use perceptions of personal and sharing partners’ usage patterns to affect risk perceptions and subsequent propensity to participate in a commercial sharing system.