U.S. oil shale deposits likely hold 1.5 trillion barrels of oil, according to Jack Dyni, a geologist emeritus at the U.S. Geological Survey. All 12 OPEC countries combined have proved crude oil reserves of about 911 billion barrels, led by Saudi Arabia, with 264.2 billion barrels, according to statistics compiled by BP Plc.

Skeptics of the potential for shale oil include Cathy Kay, an organizer for the environmental group Western Colorado Congress, who says the techniques will drain water supplies, scar the landscape and require so much power the skies will be choked with smoke from coal-fed generators.

"They are going to do absolutely massive environmental damage," said Kay, a South Africa native who's been spearheading the Grand Junction, Colo., group's anti-shale campaign since September.

"Why don't these companies invest these giant sums of money developing the cheapest, cleverest solar panel or geothermal process, instead of chasing this elusive oil?" Kay asked.

Shell, based in the Hague, estimates it can extract oil from Colorado shale for $30 a barrel, less than half the recent price of about $66 for benchmark New York futures.

Shell's process includes surrounding each shale field with an underground wall of ice. The so-called freeze walls are to prevent groundwater from swamping the heating rods and to protect the local water supply from contamination as the organic material in the rocks turns to oil, according to Terry O'Connor, the Shell vice president in charge of the company's Colorado shale project.

500,000 barrels

"There's a lot of testing to be done," O'Connor said in a May 24 interview. "We're proceeding cautiously."

O'Connor declined to say how much oil Shell expects it could produce from shale. Stark at IHS and other analysts said Shell expects to get 500,000 barrels a day from its project, 25 percent more than comes from Alaska's Prudhoe Bay, the largest U.S. oil field.

"This is an amazing resource," said James Bartis, an oil analyst at Rand, based in Santa Monica, Calif. Bartis says that success in the Rockies could cut crude prices by 5 percent, saving American consumers $20 billion a year.

"It's been raised before as a panacea for impending shortages, but never before has it been shown to be competitive with conventional oil," Bartis said.

Drillers, pipe-makers and metal fabricators such as Nabors Industries Ltd. and closely held UOP LLC will be the first to profit as Shell, Chevron and Exxon drill thousands of wells a half-mile underground by 2011.

The oil companies may begin pumping commercial quantities of oil from Colorado shale within a decade, about as long as Chevron will need to develop the 500 million-barrel Jack prospect in the deepwater Gulf of Mexico, according to Stark, who is a former Mobil Corp. geologist.