OPEC

The Organization of the Petroleum Exporting Countries (OPEC) is a group of thirteen countries made up of Islamic Republic of Iran, Iraq, Kuwait, Qatar, Saudi Arabia, the United Arab Emirates, Socialist People's Libyan Jamahiriya, Algeria, Nigeria, Angola, Venezuela and Ecuador.

OPEC's ability to control the price of oil has diminished somewhat since then, due to the subsequent discovery and development of large oil reserves in the Gulf of Mexico and the North Sea, the opening up of Russia, and market modernization. OPEC nations still account for two-thirds of the world's oil reserves, and, as of March 2008, 35.6% of the world's oil production, affording them considerable control over the global market. The next largest group of producers, members of the OECD and the Post-Soviet states produced only 23.8% and 14.8%, respectively, of the world's total oil production. As early as 2003, OPEC members had little excess pumping capacity resulted their influence on crude oil prices begin to slip.

source: http://en.wikipedia.org/wiki/OPEC