A great deal of the world's oil comes from Middle Eastern countries—Saudi Arabia, Iraq, Iran, Kuwait, and the United Arab Emirates. The natural resource is used for heating, lighting, and transportation, and for making medicines, plastics, and other goods.

To reach oil deposits underground or beneath the seafloor, oil wells are drilled. Pumps bring the oil to the surface, where it is transported to refineries. There, unwanted substances are stripped from the oil, and the final product is shipped out. Often, oil pipelines are built to funnel the oil to refineries or to ships and railroads.

Vital to the world economy, oil has the power to make poor countries rich. The former Soviet republic of Kazakhstan, for instance, is now developing its vast oil reserves. One oil field, the Kashagan field extending beneath the Caspian Sea, could yield 7 billion to 13 billion barrels of oil, experts say.

The booming industry has created many jobs in Kazakhstan, but it also has consequences for the environment. Oil drilled in the Caspian can leak into the water, hurting marine life.

Oil is also important in Iran, which depends on it for up to 85 percent of its export earnings. And Russia has become one of the world's biggest oil producers, pumping about nine million barrels a day.

Asian countries also use a lot of oil. Japan and China are the world's largest oil users. By 2025 China could be using up to ten million barrels of oil a day. Most of that will be imported.

Many experts stress that oil dependence should be lessened before the world's reserves are used up. Geologists differ on when that will be, but all agree that the Earth's supply is not unlimited—once the oil is gone, it's gone.