This is the VOA Special English Economics Report.

When we think of oil, the part of the world that comes to mind first may be the Middle East. But petroleum development takes place worldwide.

Nigeria, for example, is the largest oil producer in Africa and the eleventh largest producer in the world. Russia is the world's second largest exporter of oil and the top exporter of natural gas.

But the country that produces and exports more oil than any other is Saudi Arabia. The Saudis hold one-fourth of the world's proven oil reserves.

Last year, Saudi Arabia and other Persian Gulf countries produced about twenty-eight percent of the world's oil supply. The United States Energy Department says they also held fifty-five percent of known reserves.

The other Gulf producers are Bahrain, Iran, Iraq, Kuwait, Qatar and the United Arab Emirates. Iran has ten percent of the world's proven oil reserves. Iraq is also estimated to have a large supply of oil, and unexplored areas may hold much more.

In nineteen sixty Iran, Iraq, Kuwait, Saudi Arabia and Venezuela formed the Organization of the Petroleum Exporting Countries. Today OPEC has twelve members. The newest is Angola which joined this year.

High oil prices have brought new attention to OPEC. Its members produce about forty percent of the world's oil. But two of the world's top three oil exporters, Russia and Norway, are not OPEC members.

Its influence may have reached a high point during the oil crisis connected to the nineteen seventy-three Arab-Israeli war. Arab oil producers boycotted the United States, western Europe and Japan because of their support for Israel.

Since then, new discoveries and increased production in areas including countries of the former Soviet Union have provided more oil.

National oil companies are estimated to control about eighty percent of the world's oil supply. In recent years, rising oil prices have led more governments to act, either directly or indirectly, to take control of their oil industries.

President Hugo Chavez has moved to nationalize oil operations in Venezuela. And in Russia, a series of actions resulted in state-owned Rosneft gaining control of reserves held by Yukos. Yukos was Russia's largest private company, until the government said it owed billions of dollars in taxes and jailed its founder, Russia's richest man.