Some 90 billion barrels of oil and a third of the world's undiscovered natural gas lie beneath an area north of the Arctic Circle, US government scientists estimate in the largest-ever survey of the energy resources there.
The US Geological Survey, which announced the findings on Wednesday, called the region, which includes parts of the United States, Russia and Canada, "the largest unexplored prospective area for petroleum remaining on Earth".
All told, the area accounts for about a fifth of the world's recoverable oil and natural gas reserves, the USGS says: 13 per cent of the oil, 30 per cent of natural gas and 20 per cent of natural gas liquids.
At today's current consumption rate of 86 million barrels a day, the yet-to-be-tapped oil in the Arctic would supply global demand for three years.
Pursuing it is sure to be controversial with environmental groups that want to protect the pristine wilderness and the area's endangered species.
The oil is considered "technically recoverable" using existing technology, but the survey did not consider the cost of overcoming obstacles to drilling, such as permanent sea ice or deep ocean waters.
Melting caused by global warming has opened up some areas that were previously considered too difficult to reach. Oil companies have already spent billions to secure leases to explore some of the uncharted waters.
About 84 per cent 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.
About a third of the oil found in the survey is off the coast of Alaska. The majority of the natural gas is concentrated in two Russian provinces.
"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, 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."