USGS sees promise in Alaskan shale WASHINGTON, Feb. 27 (UPI) -- There is "great promise" in the oil and natural gas reserves potentially available in shale deposits in Alaska's North Slope, the U.S. government said. The U.S. Geological Survey estimated there were as much as 2 billion barrels of oil and 80 trillion cubic feet of natural gas in onshore shale resources in Alaska's North Slope. "Alaska's energy resources hold great promise and economic opportunity for the American people and we will continue to expand our scientific understanding of existing resources as part of our commitment to an all-of-the-above energy approach that includes safe and responsible production of American oil and gas resources," U.S. Secretary of the Interior Ken Salazar said in a statement. The USGS said production of shale oil and natural gas has never been attempted in the North Slope because of "economic and infrastructure considerations." USGS estimates varied widely, starting at no reserve potential. "Better knowledge of the untapped resource potential found in all areas of the country will help us better make science-based decisions about how we continue to grow domestic energy production for America," added Salazar. The United States has some of the richest deposits of shale natural gas in the world. Critics say the extraction method, known as fracking, poses a threat to water supplies.