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A true duopoly (from Greek dyo / δυο (two) + polein / πωλειν (to sell)) is a specific type of oligopoly where only two producers exist in one market. In reality, this definition is generally used where only two firms have dominant control over a market. In the field of industrial organization, it is the most commonly studied form of oligopoly due to its simplicity.


Duopoly models in economics

There are two principal duopoly models, Cournot duopoly and Bertrand duopoly:

  • The Cournot model, which shows that two firms assume each others output and treat this as a fixed amount, and produce in their own firm according to this.
  • The Bertrand model, in which, in a game of two firms, each one of them will assume that the other will not change prices in response to its price cuts. When both firms use this logic, they will reach a Nash Equilibrium.


Modern American politics has been described as a duopoly since the Republican and Democratic parties have dominated and framed policy debate as well as the public discourse on matters of national concern for about a century and a half. Third Parties have encountered various blocks in getting onto ballots at different levels of government as well as other electoral obstacles, more so in recent decades.

See List of political parties in the United States for a more comprehensive look at the politics of the Two-party system, Duverger's law.

Examples in business

The most commonly cited duopoly is that between Visa and Mastercard, who between them control a large proportion of the electronic payment processing market. In 2000 they were the defendants in a US Department of Justice antitrust lawsuit.[1][2] An appeal was upheld in 2004.[3]

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