The Organization of Petroleum Exporting Countries or OPEC is an intergovernmental organization comprising twelve oil-producing countries, predominantly from the Middle East and South America, who currently control around 79 percent of global crude oil reserves. It aims to control the supply of oil in an effort to stabilize the price of oil on the world, giving regard to the interests of producing nations. It is considered a cartel that exercises considerable control over world oil production and prices. However, its ability to determine the price of oil has relatively diminished, due to discovery and development of large oil reserves in Alaska, the North Sea, Canada, the Gulf of Mexico and Russia.
See: OPEC website