WASHINGTON – Some 90 billion barrels of oil and nearly a third of the world's undiscovered natural gas remain untapped under an area north of the Arctic Circle, government scientists estimate, in the largest-ever survey of the area's energy potential.

All told, the area accounts for about a fifth of the world's undiscovered, technically recoverable oil and natural gas reserves, the U.S. Geological Survey reported: 13 percent of the oil, 30 percent of natural gas and 20 percent of the natural gas liquids.

The oil is considered “technically recoverable” using existing technology, but the USGS did not consider the cost of overcoming obstacles to drilling, such as permanent sea ice or deep ocean waters. About 84 percent of the undiscovered oil and gas is offshore, the USGS estimated, but much of it is close enough to land to fall under national territorial claims.

Much of the oil is off the coast of Alaska or in Russian provinces.

More than half of the oil reserves are believed to occur in three geologic areas – the West Siberian Basin, the East Barents Basins and Arctic Alaska.

“Before we can make decisions about our future use of oil and gas and related decisions about protecting endangered species, native communities and the health of our planet, we need to know what's out there,” USGS Director Mark Myers said in releasing the report Wednesday, the product of a four-year study.

“With this assessment,” he said, “we're providing the same information to everyone in the world so that the global community can make those difficult decisions.”