Denver (AP) - The U.S. Geological Survey now estimates the Piceance Basin in western Colorado has 50 percent more oil shale than it thought 20 years ago.
USGS said Thursday it revised its estimate to about 1.5 trillion barrels of in-place oil shale after looking at new areas that previously had too little data for research.
Interior Secretary Ken Salazar says the new estimate demonstrates the need for research and development.
Companies are still working to find the most economical way to extract the oil, a process that requires energy to bake the rock and pump oil to the surface.
The Piceance Basin contains one of the thickest and richest oil shale deposits in the world.
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