(CNN) -- Here's a look at the Organization of the Petroleum Exporting Countries, headquartered in Vienna, Austria.
Facts: The purpose of OPEC for members is to "co-ordinate and unify their petroleum policies in order to promote harmony and stability in the oil market."
OPEC members collectively supply about 40% of the world's oil supply.
Together, OPEC members control about 75% of the world's total proven crude reserves.
OPEC member countries monitor the market and decide collectively to raise or lower oil production in order to maintain stable prices and supply.
A unanimous vote is required on raising or lowering oil production.
Each member country controls the oil production of its country, but OPEC aims to coordinate the production policies of member countries.
Oil and energy ministers from OPEC member countries usually meet twice a year in March and September to determine OPEC's output level. They also meet in extraordinary sessions whenever required.
Current Members: Algeria - 1969-present
Angola - 2007-present
Ecuador - 1973-1992, 2007-present
Iran - 1960-present
Iraq - 1960-present
Kuwait - 1960-present
Libya - 1962-present
Nigeria - 1971-present
Qatar - 1961-present
Saudi Arabia - 1960-present
United Arab Emirates - 1967-present
Venezuela - 1960-present
Former Members: Gabon - 1975-1994
Indonesia - 1962-2009
Timeline: September 14, 1960 - OPEC is formed in Baghdad, Iraq, by founding members Iraq, Kuwait, Iran, Saudi Arabia and Venezuela.
November 6, 1962 - OPEC is registered with the United Nations Secretariat (U.N. Resolution No 6363).
1973-1974 - Due to United States support of Israel in the Arab-Israeli conflict, the members of OPEC decide to raise the cost of oil from $3/barrel to around $12/barrel.
October 1973 - OPEC issues an embargo against the U.S., halting oil exports. Customers in the U.S. experience long lines at gas stations and at times cannot find gas at all. Prices go from 36 cents a gallon in 1972 to over 50 cents a gallon in 1973.
March 18, 1974 - At an OPEC meeting, seven members lift the ban on exports to the U.S.: Algeria, Saudi Arabia, Kuwait, Qatar, Bahrain, Egypt and Abu Dhabi. Libya and Syria refuses to drop the ban, and Iraq boycotts the talks.
December 31, 1974 - Libya lifts its 14-month-old oil embargo against the U.S.
November 2007 - Ecuador rejoins OPEC after a 15-year absence.
May 2008 - Indonesia announces that it will leave OPEC in 2009. The country is currently a net importer of oil, due to falling production from aging wells.
January 1, 2009 - Indonesia suspends its membership in OPEC.