Beneath Melting Arctic Ice, Stores of OilIce floats on the surface of Alaska's Beaufort Sea—and oil lies beneath. The U.S. Geological Survey estimates that the Arctic holds 13 percent of the world's undiscovered oil, some 90 billion barrels that might be produced with existing technologies. But extreme conditions here will put conventional petroleum practices to the test.(Related: "The Next Prospects: Four Offshore Drilling Frontiers")Most of the Arctic's undiscovered oil is thought to lie offshore under less than 1,640 feet (500 meters) of water in some of the most remote places on Earth. The closest U.S. Coast Guard Air Station to the Beaufort Sea is some 950 miles (1,530 kilometers) away and the nearest major port lies 1,300 nautical miles (2,400 kilometers) distant.(Full Coverage: "Gulf Oil Spill: One Year Later")

Drilling will be difficult in this remote realm of frigid temperatures, high seas, shrieking winds, darkness, sea ice, and minimal visibility. And environmentalists worry that responding to spills here will be difficult or impossible, putting the region's unique ecosystem at lasting risk.After a legal challenge by Native Alaskans and environmentalists delayed necessary federal clean air permits, Shell* postponed plans to drill in the Beaufort Sea this summer and is now aiming to explore the area in 2012. Outside U.S. waters, Arctic oil exploration is already under way.—Brian Handwerk* This story is produced as part of National Geographic’s Great Energy Challenge initiative, sponsored by Shell. National Geographic maintains autonomy over content.

Photograph by Paul Nicklen, National Geographic

Pictures: Four New Offshore Drilling Frontiers

With new technology, oil companies have extended the reach of their operations off the coastline and into deep water. See four of the offshore frontiers that may be supplying tomorrow's oil.

April 20, 2011