The decision comes despite comments from state and federal agencies and environmentalists that threats to air and water were understated or not adequately analyzed.

Shell Frontier Oil & Gas Co., Chevron USA and EGL Resources applied for 160-acre parcels for research and development projects in Rio Blanco County. The three companies, along with the Oil Shale Exploration Co. in Utah, were the finalists in competition for the leases, and will be in line for commercial projects.

Although the decision authorizes the 10-year leases, the companies must submit detailed development plans, monitor groundwater, obtain all required permits to protect such resources as air and water quality before and agree to various conditions, the Interior Department said.

Work could start as early as next summer.

Earlier this year, the Bureau of Land Management released environmental assessments saying the projects would have no significant environmental impacts. The announcement by C. Stephen Allred, assistant Interior secretary for land and minerals management, means the Interior Department agrees.

Not in agreement were the White River National Forest supervisor and the Colorado Department of Public Health and Environment, which said the BLM had understated threats to air quality in the Flat Tops Wilderness.

In comments obtained by Boulder-based Western Resource Advocates through the Freedom of Information Act, the Colorado Division of Wildlife said all the projects, including Shell's three parcels of 160 acres each, are in or next to elk and mule deer winter and summer range and migration routes and sage grouse habitat.