Here, there are only two producers of a commodity which has several buyers.
A true duopoly 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.
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. An appeal was upheld in 2004.
Examples where two companies control a large proportion of a market are:
•    Pepsi vs Coca-Cola in soft drink market
•    Gillette vs Schick in razor blade market
•    Airbus vs Boeing in commercial jet aircraft market
•    Sotheby's vs Christie's in diamond auctions
•    Marvel Comics vs DC Comics in comic books
•    Sirius vs XM in the satellite radio market
•    Intel vs AMD in the Microprocessor market
•    The local cable company vs the local telephone company in residential broadband Internet access
•    Vodafone vs Mobinil in the Egyptian mobile market
•    Telecom vs Vodafone in the New Zealand mobile market
•    Kodak vs Fujifilm in motion picture film stock market
•    K-Kauppa vs S-Group in the Finnish supermarket market (jointly they control 75% of supermarket market)
•    Foodstuffs vs Progressive Enterprises in the New Zealand supermarket market (joinly they control 90% of supermarket market)
•    PetroChina vs Sinopec in Chinese oil production.