Colorado and Utah have as much oil as Saudi Arabia, Iran, Iraq, Venezuela, Nigeria, Kuwait, Libya, Angola, Algeria, Indonesia, Qatar and the United Arab Emirates combined.

That's not science fiction. Trapped in limestone up to 200 feet thick in the two Rocky Mountain states is enough so-called shale oil to rival OPEC and supply the U.S. for a century.

Exxon Mobil Corp. and Chevron Corp., the two biggest U.S. energy companies, and Royal Dutch Shell Plc are spending $100 million a year testing new methods to separate the oil from the stone for as little as $30 a barrel. A growing number of industry executives and analysts say new technology and persistently high prices make the idea feasible.

"The breakthrough is that now the oil companies have a way of getting this oil out of the ground without the massive energy and manpower costs that killed these projects in the 1970s," said Pete Stark, an analyst at IHS Inc., an Englewood, Colo., research firm. "All the shale rocks in the world are going to be revisited now to see how much oil they contain."

The U.S. imports two-thirds of its oil, spending $300 billion a year, or 40 percent of the record trade deficit. Every $10 increase in a barrel of crude costs an American household $700 a year, according to the Rand Corp., founded in 1946 to provide research for the U.S. military. Oil prices have risen 63 percent since 2004, and higher fuel costs have slowed growth in the world's largest economy to the lowest in four years.

The last effort to exploit the Colorado and Utah shale fields foundered in the 1980s after crude prices tumbled 72 percent, resulting in a multibillion-dollar loss for Exxon. Techniques developed to coax crude from tar sands in Alberta, 1,600 miles to the north, may help the U.S. projects' engineers.

"The potential for shale is large," said Joseph Stanislaw, senior energy adviser for Deloitte & Touche LLP and co-author with oil analyst Daniel Yergin of "The Commanding Heights: The Battle for the World Economy" (Simon & Schuster, 464 pages, $26). "Assuming the technology proves out, the size and scale of the reserves are significant."

Energy providers are investing in shale oil production because the reserves are large enough to generate higher returns than smaller fields in Oklahoma and Texas, where output is declining after eight decades.

Shale is also a more attractive investment than new U.S. refineries, which Shell and Chevron say may lose money as rising use of crop-based fuels such as ethanol lowers domestic gasoline demand. Exxon says it isn't interested in building new fuel plants in the U.S. because the company expects North American fuel consumption to peak by 2025.