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The four firm concentration ratio (CR4) is a measure of market concentration which is calculated by adding the market share of the four largest firms in a given industry. A CR4 number of higher than 50 percent is generally considered to be a concentrated market, with numbers ranging above 75 percent considered to be oligopolistic. In 2017, the United States had two industries where four or fewer firms completely controlled the market, namely Secondary Market Financing and Other Depository Credit Intermediation. Other notable concentrated industries included Tobacco Manufacturing (dominated by Philip Morris International, Altria Group and British American Tobacco) and Aircraft Manufacturing (dominated by Boeing and Airbus).