This document discusses the concept of oligopoly, which refers to a market structure with a small number of firms producing similar or identical products. The key feature of oligopoly is the tension between cooperation and self-interest among firms. While cooperating to act as a monopolist would be most profitable, firms have an incentive to compete by increasing their own production. As a result, oligopolies typically produce more and charge lower prices than a monopoly, but less and higher than a competitive market. Game theory, such as the prisoner's dilemma, demonstrates why cooperation is difficult to maintain in oligopolies.