In a wide-ranging study published in 2000, the U.S. Geological Survey estimated that ultimately recoverable resources of conventional oil totaled about 3.3 trillion barrels, of which a third has already been produced. More recently, Cambridge Energy Research Associates, an energy consultant, estimated that the total base of recoverable oil was 4.8 trillion barrels. That higher estimate — which Cambridge Energy says is likely to grow — reflects how new technology can tap into more resources.

“It’s the fifth time to my count that we’ve gone through a period when it seemed the end of oil was near and people were talking about the exhaustion of resources,” said Daniel Yergin, the chairman of Cambridge Energy and author of a Pulitzer Prize-winning history of oil, who cited similar concerns in the 1880s, after both world wars and in the 1970s. “Back then we were going to fly off the oil mountain. Instead we had a boom and oil went to $10 instead of $100.”

There is still a minority view, held largely by a small band of retired petroleum geologists and some members of Congress, that oil production has peaked, but the theory has been fading. Equally contentious for the oil companies is the growing voice of environmentalists, who do not think that pumping and consuming an ever-increasing amount of fossil fuel is in any way desirable.

Increased projections for how much oil is extractable may become a political topic on many different fronts and in unpredictable ways. By reassuring the public that supplies will meet future demands, oil companies may also find legislators more reluctant to consider opening Alaska and other areas to new exploration.

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On a global level, the Organization of the Petroleum Exporting Countries, which has coalesced around a price of $50 a barrel for oil, will likely see its clout reinforced in coming years. The 12-country cartel, which added Angola as its newest member this year, is poised to control more than 50 percent of the oil market in coming years, up from 35 percent today, as Western oil production declines.