BILLINGS, Mont. - Oil and gas drilling on federal lands across the Rocky Mountain West could increase by more than 160 percent over the next two decades due in part to pro-industry regulations enacted by the Bush administration, according to a report released Monday by an environmental group.

The Washington, D.C.-based Wilderness Society analyzed drilling plans and said oil and gas exploration was poised to push into some of the West's most environmentally sensitive areas. That includes plans to drill in Colorado's Roan Plateau, the Upper Green River Basin in Wyoming and Montana's portion of the Powder River Basin.

"The impacts of this type of development would be truly staggering. It would likely well exceed 1 million acres," said the Wilderness Society's Nada Culver, who wrote the report. "This is the time to take a step back and consider what current levels of drilling are already doing to our public and private lands."

At least one federal official questioned the accuracy of the report, arguing it appeared to be based partially on plans that are not yet final.

More than 126,000 new oil and gas wells have been approved or are under review for federal lands in Wyoming, Colorado, Montana, Utah and New Mexico, according to the Wilderness Society report. Wyoming would see the most activity: 58,000 new wells.

By comparison, the five states had 77,000 wells producing oil or natural gas as of earlier this year.