SAN FRANCISCO -- Opponents in a long-running debate over when the world will run out of oil squared off Tuesday in a crowded room of scientists, reaching only one conclusion: The supply of fossil fuels is fixed and the world economy will eventually have to wean itself from oil.

The most dire and perhaps speculative forecast calls for global oil production to peak next year -- specifically on Thanksgiving.

Others say the end can't be accurately predicted, but that it is likely decades rather then centuries away, and that the consequences will be grave: huge inflation, global resource wars -- China vs. the United States was emphasized as a possibility -- and the end of civilization as we know it.

Other experts at the face-off, held here during a meeting of the American Geophysical Union, said there is nothing to worry about in the short term.

U.S. peaked already

The argument stretches back to a 1956 prediction by M. King Hubbert that oil production in the lower 48 U.S. states would peak in the early 1970s. He was right. The United States now imports nearly 60 percent of the oil it uses.

Kenneth Deffeyes, a Professor Emeritus at Princeton University, has taken Hubbert's logic a step further and predicts the world's oil production will top out late in 2005.

"It's Thanksgiving plus or minus three weeks," said Deffeyes, who grew up in the oil fields and was a researcher at Shell Oil for several years.

Deffeyes second book on the topic, "Beyond Oil: The View from Hubbert's Peak" (Hill and Wang) is due out in March. His crystal ball is full of complex formulas and, most scientists agree, numbers that are impossible to accurately pin down, such as the amount of oil in known fields and how much more will be found.

"This is not science," said Michael Lynch, a political scientist and energy consultant. "This is forecasting."

Lynch agrees there are problems with relying so heavily on oil, and he sees more price volatility ahead. But he argues that many smaller deposits will be found and they will add up to "a lot of oil" over time. He also faults the running-dry-soon predictions as being based not on geology, but on politics and economics: Oil production in various countries has flattened or fell at certain times for reasons having nothing to do with how much they could produce, Lynch says.

Further, Lynch contends, it is not possible to predict the discovery of new oil fields or the true size of existing in-ground reserves. He likens current oil forecasts to stock market prediction. Charts fit history well, he says, "but they're not predictive."

Alternatives?

Likewise, analyst Bill Fisher of the University of Texas at Austin sees plenty of oil over the next few decades. Fisher sees no reason to panic. He expects the world to gradually transition to an economy based on natural gas during the first half of this century, then to a hydrogen economy before 2100. He pointed out that estimates of oil reserves tend to grow over time, no matter who does the guessing.

The debate got more complex at this point.

Caltech physicist David Goodstein sees little hope for hydrogen, which he said requires fossil fuels in order to extract. And natural gas, like oil and coal and shale (another proposed alternative) are all finite, Goodstein argues.

"The oil will run out," he said. "The only question is when."

Goodstein puts little stock in nuclear fusion, which for decades has been proposed as the cousin of fission with unlimited potential. "Fusion and shale oil are the energy sources of the future, and they always will be," he quipped. Solar energy shows promise, he said, but "we haven't figured out how to use it."

So Goodstein takes a pragmatic approach. It doesn't matter so much when we run out, he argues, but what we do about it.

Global trap

Goodstein, author of the book "Out of Gas: The End of the Age of Oil" (W.W. Norton & Company) sees a looming world crisis that could fuel war and bring society to its knees.

"We have created a trap for ourselves," Goodstein said.

The United States has so far avoided serious consequences from the trap by relying on imports. The country uses about 7 billion of the 30 billion barrels of oil produced annually around the globe. And it makes us rich. Oil consumption equals standard of living, experts agree.

Meanwhile, other countries are beginning to clamor for oil at unprecedented rates, and therein lies the recipe for potential disaster.

China uses a comparatively modest 1.5 billion barrels a year (perhaps 2.4 billion this year) according to some estimates. India consumes less. Both countries' economies are becoming increasingly dependent on oil, however. China's consumption is expected to grow 7.5 percent per year, and India's 5.5 percent, according to the Institute for the Analysis of Global Security.

By 2060, oil production will have to triple just to meet global population growth and maintain current standards of living, said Stanford University geophysicist Amos Nur.

Yet China's own production has been flat since the 1980s and it now imports 40 percent of what it needs.

'When do we panic?'

"What matters in the short term is, when do we panic?" Nur said. "In my opinion, the point of panic has already taken place."

It's a behind-the-scenes sort of panic. The two largest economies on Earth -- China and the United States -- have already incorporated the finite nature of oil into their national security policies, Nur argues, citing policy statements from both governments reflecting the need to secure stability in oil-producing countries and a free flow of the resource. The war in Iraq, a country second only to politically unstable Saudi Arabia in oil reserves, is another clue, he said.

"There is a huge conflict that might be emerging," Nur said.

Some of the fine points of the various presentations were argued, even resulting in one shouting match over how much oil is in Saudi Arabia. But none of the roughly 500 scientists in the room voiced disagreement with Nur's view of the potential for war.

If the world is sliding toward global conflict over oil, the skids may be pretty well greased, politically speaking.

Governments do not have the political will to prepare for the end of oil, says Goodstein, the Caltech physicist.

"Civilization as we know it will come to an end sometime this century, when the fuel runs out," Goodstein said, adding that "I certainly hope my prediction is wrong."