"Seven Sisters" was a common term for the seven transnational oil companies of the "Consortium for Iran" oligopoly or cartel, which dominated the global petroleum industry from the mid-1940s to the mid-1970s. The oligopoly lasted until the 1970s when OPEC and national oil companies gained control over the key governing arrangements for oil production. The companies used interlocking ownership of oil fields to maintain collusion and restrict oil supply, so that the companies would reap greater profits.
Alluding to the seven mythological Pleiades sisters fathered by the titan Atlas, the business usage was popularized in the 1950s by businessman Enrico Mattei, head of the Italian state oil company Eni. The industry group consisted of:
- Anglo-Iranian Oil Company (originally Anglo-Persian; now BP)
- Royal Dutch Shell (now Shell)
- Standard Oil Company of California (SoCal, later Chevron)
- Gulf Oil (now merged into Chevron)
- Texaco (now merged into Chevron)
- Standard Oil Company of New Jersey (Esso, later Exxon, now part of ExxonMobil)
- Standard Oil Company of New York (Socony, later Mobil, now part of ExxonMobil)
Preceding the 1973 oil crisis, the Seven Sisters controlled around 85 per cent of the world's petroleum reserves. In the 1970s, many countries with large reserves nationalized holdings of all major oil companies. Since then, industry dominance has shifted to the OPEC cartel and state-owned oil and gas companies in emerging-market economies, such as Saudi Aramco, Gazprom (Russia), China National Petroleum Corporation, National Iranian Oil Company, PDVSA (Venezuela), Petrobras (Brazil), and Petronas (Malaysia). In 2007, the Financial Times called these "the new Seven Sisters". According to consulting firm PFC Energy, by 2012 only 7% of the world's known oil reserves were in countries that allowed private international companies free rein. Fully 65% were in the hands of state-owned companies.