Glossary of competition terms

This Glossary was prepared by DG COMP and the OECD for non-competition specialists. Each term is enriched with references of national case laws from the e-Competitions Bulletin. (© European Union - © OECD)

Cournot (Nash) Equilibrium

The Cournot model of oligopoly assumes that rival firms produce a homogenous product, and each attempts to maximize profits by choosing how much to produce. All firms choose output (quantity) simultaneously. The basic Cournot assumption is that each firm chooses its quantity, taking as given the quantity of its rivals. The resulting equilibrium is a Nash equilibrium in quantities, called a Cournot (Nash) equilibrium.

The Cournot model provides results which are of some importance to industrial economics. First of all, it can be shown that price will not in most cases equal marginal costs (see costs) and Pareto efficiency is not achieved. Moreover, the degree to which each firm’s price exceeds marginal cost is directly proportional to the firm’s market share and inversely proportional to the market elasticity of demand.

If the oligopoly is symmetric, that is all firms have identical products and cost conditions, then the degree to which price exceeds marginal cost is inversely related to the number of firms. Thus, as the number of firms increases, the equilibrium approaches what it would be under perfect competition. More generally, it can be shown that for the industry the degree to which price exceeds marginal cost is directly proportional to the Herfindahl-Hirschman Index of concentration. As concentration rises, industry performance deviates more from the norm of perfect competition. (...)

See also Bertrand (Nash) equilibrium.

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