Common Knowledge of Price and Expected Cost in an Oligopolistic Market

If a stochastically monotone aggregate of asymmetrically informed agents' expectations of a random variable is common information, then the agents must agree on their expectations. This result is applied to a model of an oligopolistic market where the firms have a common random component of cost. It makes possible a characterization of the naive Cournot-Nash and Bayes-Cournot equilibria where the price is common knowledge. On this basis the existence of rational expectations equilibria is shown, the full communication equilibria are characterized, and the question of uniqueness is answered.