"US companies have developed and patented new technologies to develop oil shale that are both economical and environmentally friendly," BLM assistant director for minerals Tom Lonnie said.

"The BLM welcomes public input as to how we can best develop this energy source, which will enable us to expand and diversify domestic energy production in accordance with the president's National Energy Plan."

Shale is a sedimentary rock containing kerogen, which can be processed and converted into synthetic oil. The BLM said the US has about half of the world's oil shale reserves. Other big reserves are located in Russia, China and Australia.

The bureau is examining several Rocky Mountain basins that are considered to have the most easily recoverable deposits in the US.

The BLM plans to issue 10-year research and development leases, but any lease could go into commercial production before the end of the term, BLM spokesman Jim Edwards said.