In a model of repeated Cournot competition under complete information, I show how the existence of a fringe of managerial firms affects the stability of a cartel of strict profit-maximizing firms. There always exists a critical dimension of the fringe that makes the cartel unstable, and this dimension is non-monotone in the total number of firms. By appropriately selecting the dimension of the fringe, a policy maker can affect the equilibrium outcome.
As an example, I consider the case of a domestic authority that is contemplating whether to allow entry of a fringe of managerial foreign firms in the domestic market to increase the competitive pressure, thereby enhancing domestic welfare.[JEL Classification: D43; L13; L21]