AMHERST, Mass. — WHILE many existing oil and gas reserves in other parts of the world are facing steep decline, the Arctic is thought to possess vast untapped reservoirs. Approximately 13 percent of the world’s undiscovered oil deposits and 30 percent of its natural gas reserves are above the Arctic Circle, according to the United States Geological Survey. Eager to tap into this largess, Russia and its Arctic neighbors — Canada, Norway, the United States, Iceland and Denmark (by virtue of its authority over Greenland) — have encouraged energy companies to drill in the region.

For Russia, which recently seized a Greenpeace ship and is prosecuting 30 of the group’s activists for attempting to scale an oil platform, the temptation to exploit the Arctic Ocean is especially powerful. Russia’s economy is heavily dependent on exports of oil and gas, and the government relies on these sales for much of its income. Until recently, the Russians could draw on reservoirs in western Siberia to satisfy their needs, but now, with many of these fields in decline, they are counting on Arctic supplies to maintain current production levels. “Our first and main task is to turn the Arctic into Russia’s resource base of the 21st century,” Dmitri A. Medvedev, then the president, declared in 2008.

The Russians have explored drilling options in several offshore areas of the Arctic. In the Pechora Sea, above northwestern Siberia, the Russian energy giant Gazprom has installed its Prirazlomnaya platform — the one protesting Greenpeace activists attempted to board. Further east, in the Kara Sea, the state-owned Rosneft is collaborating with ExxonMobil to develop promising deposits; Rosneft has also teamed up with Statoil of Norway and Eni of Italy to investigate prospects in the Barents Sea.

But Russia is hardly alone in seeking to exploit the Arctic. Norway, like Russia, derives considerable income from gas and oil exports and is under pressure to develop reserves in the Barents Sea to compensate for the decline of its existing fields in the North and Norwegian Seas. Other areas of the Arctic are also being eyed for development. Cairn Energy of Edinburgh has sunk exploratory wells in waters off Greenland, for example, while Royal Dutch Shell is attempting to develop fields off Alaska.