Organization of Petroleum Exporting Countries (OPEC), international organization primarily concerned with coordinating the crude-oil policies of its member states. Founded in 1960, OPEC has 11 members--Algeria, Indonesia, Iran, Iraq, Kuwait, Libya, Nigeria, Qatar, Saudi Arabia, United Arab Emirates, and Venezuela. Two countries joined OPEC and later ended their membership in the organization: Ecuador joined in 1973 and left in 1992, and Gabon became a member in 1975 and terminated its membership in 1995. OPEC headquarters is located in Vienna, Austria. The organization's authority is the Conference, made up of high-level representatives of the member governments, which meets at least twice a year. The board of governors implements resolutions of the Conference and manages the organization.

In the late 1950s, the amount of oil produced worldwide was greater than demand. The price of oil, which was controlled by the oil companies, dropped and with it dropped the amount of money the oil companies paid the oil-producing nations. OPEC was formed in reaction to this drop in payments. In addition to joining OPEC, some oil-producing countries nationalized the oil production and refining equipment of the oil companies, which generated large amounts of income for those countries.

In the 1970s, as oil supplies in non-OPEC countries were reduced, the organization raised the price of oil. Another price-control tactic used by OPEC is to set production ceilings that specify how much oil may be produced by each member country. In the 1980s some OPEC nations ignored the production ceilings and this resulted in overproduction and a drop in oil prices. The organization has also used the supply of oil as a political tactic—for example, stopping delivery of oil to nations supporting Israel in the Arab-Israeli War of 1973—a tactic that resulted in oil and gasoline shortages in many Western nations.