Alaska's North Slope shales may hold as much as 80 trillion cubic feet of gas, or more than half the highest estimate for the Marcellus formation, and as much as 2 billion barrels of oil, the U.S. Geological Survey said.

President Barack Obama's administration and the state of Alaska are offering more access to oil and natural gas resources on land and in the Arctic waters to help lower dependence on imported fuel and push more crude through a major oil pipeline crossing the state. Royal Dutch Shell Plc (RDSA) plans to start drilling this year in the Chukchi and Beaufort seas, which are off the coast of the North Slope.

"Alaska's energy resources hold great promise and economic opportunity for the American people," Interior Secretary Ken Salazar said today in an e-mailed statement.

The geological service, part of the Interior Department, said in a statement that North Slope shale hasn't been developed because of economic and infrastructure considerations.

The assessment, the first made of North Slope shale resources, is based on success in extracting oil and gas from similar formations, such as the Marcellus Shale in the U.S. East. The agency last year estimated Marcellus may hold as much as 144 trillion cubic feet of gas.

Shale gas and shale oil, produced by horizontal drilling and hydraulic fracturing by injecting water and chemicals underground, led to record natural gas output in the U.S. last year and 33 percent decline in prices in the past 12 months.

To contact the reporter on this story: Katarzyna Klimasinska in Washington at [email protected]

David Fuller's view With rising petrol prices, an election to contest in November and less idealism about the short to medium-term potential for renewable energy, the White House is adopting a more commercial stance towards the development of the USA's abundant reserves of gas and oil.