The death of cheap, abundant crude, peak forecasters warn, might unleash war and plunge the world into a second Great Depression.

That’s not the prophecy of some apocalyptic cult. Willem Kadijk, a hedge fund adviser, is just one new proponent of a geologic theory known as peak oil. Behind this controversial idea is the belief that global oil production is now at or near its zenith. Once the flow crests and starts to decline — and some geologists say it already has — oil will no longer be able to slake the world’s growing thirst for energy. The result will be the oil shock to end all oil shocks. The price of a barrel of crude will spiral to $200 — and keep rising. To the peaksters, today’s energy crunch is nothing next to the pain that will follow.

“Peak oil is a reality,”said Mr. Kadijk, a senior equity salesman at Kepler Equities, an Amsterdam-based brokerage. He plans to start a fund to capitalize on what he sees as a looming crisis for the world’s fossil fuel-based economy and the ultimate bull market in oil.

As energy prices soar and violence convulses the Middle East, the peak-oil movement — an unlikely alliance of geologists, physicists, oil industry consultants and environmental activists — is winning converts. Peak-oil ideas are bubbling up from scientific journals and offbeat Web sites, much the way warnings of global warming did a decade ago. For the first time, the peaksters have begun to grab the attention of Washington and Wall Street.

Nonsense, said Russ Roberts, a spokesman for Exxon Mobil Corp., the world’s largest oil company. Exxon Mobil, which has reaped record profits as the price of oil has surged, has taken out advertisements dismissing peak oil in American newspapers.