"The world produces about 85 million barrels a day," Mr. Pickens said. "That's where demand is now, too. And I've seen forecasts that demand is going to be higher than that by the end of the year."

What's more, Mr. Pickens added, pre-Hurricane Katrina refining capacity was already at the breaking point, which is another point that is pretty unarguable. "Refineries were operating at 96 percent," he said. "You can't operate anything at 96 percent. It'll start breaking down."

That last paragraph, though, encapsulates the world view of the peakists: all the easy deals have been done. One reason refineries are operating at such high capacity is that no new refineries have been built in the United States for some 30 years, which Mr. Simmons believes can be attributed to the shortsightedness of the industry. "My theory was that if the industry didn't expand like crazy the U.S. would find itself running short of energy." It didn't, and we are.

Even more troubling, the pessimists believe that it is going to be increasingly difficult to replace the oil that we're now using up. "Let me give you a number that is pretty shocking when you hear it," Mr. Pickens said. "The world uses 30 billion barrels of oil a year. There is no way we're replacing 30 billion barrels of oil. Just a million barrels a day is 1,000 wells producing 1,000 barrels. That's big."

How do the economists counter the geologists' arguments? They don't deny that it is hard to find new oil. But they believe that whenever tight supplies push up the price of oil, the rising price itself becomes our salvation. For one thing, higher prices temper demand as people begin to change their energy habits. (Mr. Pickens believes this as well.) Surprisingly, this has not yet happened even as gasoline at the pump has more than doubled in the last year or so. But inevitably, there will come a point when it will change behaviors.

Secondly, they believe higher prices spur innovation. Oil that couldn't be extracted profitably at, say, $15 a barrel, can be enormously profitable at $60 a barrel. In the view of Mr. Yergin and his allies, in fact, this is exactly what has been happening. They point to new oil that is coming out of the Caspian Sea, deepwater drilling in Brazil and the oil sands in northern Alberta as examples. The 16 million barrels a day of new oil Mr. Yergin expects to see by 2010, he told me, "is predicated on $25-to-$30 oil." If oil stays higher than that, then there will be even more investment, and not just in ways to extract oil, but in new refineries and pipelines and other infrastructure.

If you mention this theory to a hard-core peakist like Mr. Simmons, you'd better be ready for an earful. "These economists are so smug," he said derisively. "All they talk about is the magic of the free market. They don't seem to understand that this is incredibly capital intensive."