#USHouseMarketStructureDraft An oligopoly is a market structure that consists of a small number of firms that have substantial influence over a certain industry or market. While the group holds a great deal of market power, no one company within the group has enough sway to undermine the others or steal market share.

In the United States, the three leading stock indexes are the Dow Jones Industrial Average, the S&P 500, and the Nasdaq Composite. For international markets, the Financial Times Stock Exchange 100 Index and the Nikkei 225 Index are popular proxies for the British and Japanese stock markets, respectively.