The U.S. Geological Survey Thursday increased its estimate of oil shale resources in the Piceance Basin in northwestern Colorado by 50% to more than 1.5 trillion barrels. The Obama administration has halted commercial lease sales of oil shale development, saying more research, particularly on the environmental consequences, is needed before moving ahead with development. The USGS said its latest assessment of the nation's largest oil shale basin, the first since 1989, didn't include a recoverable resource estimate, however, because the resource is currently not economical to recover and there are still a number of environmental concerns about development.