Common pool resources present a challenging problem for management institutions. The tragedy of the commons, the externality associated with common pool resources, results in inefficient competitive equilibria. The over-exploitation of scarce resources and over-investment by resource extractors are a result of this externality. Fisheries are a commonly cited case study for this phenomenon. Expanding on the past work illustrating how monopolistic market power can result in more efficient outcomes than open-access regimes, this paper describes the theoretical impacts of intermediate levels of market power in fisheries. By modeling Cournot competition in a theoretical fishery, I compare the steady-state outcomes of a social planner, monopolist, and oligopoly. The findings of this analysis suggest that there always exists an N-firm oligopoly that has a steady-state stock and harvest that is indistinguishable from a welfare-maximizing social planner.