ExxonMobil has signed an agreement with Russian oil firm Rosneft to explore for offshore oil in the Russian part of the Arctic Ocean.
In return, Rosneft will take part in Exxon operations in the Gulf of Mexico and onshore in Texas, The New York Times says.
The Arctic oil exploration deal supersedes a similar partnership reached between Rosneft and BP, the British oil giant, earlier this year. BP's deal was blocked by the billionaire partners in another BP venture in Russia, according to Reuters.
Russian Prime Minister Vladimir Putin announced the deal in the Russian resort town of Sochi on the Black Sea, and said that total investments under the agreement could reach $500 billion, although the exact details of this were unclear.
"New horizons are opening up. One of the world's leading companies, ExxonMobil, is starting to work on Russia's strategic shelf and deepwater continental shelf," Putin said, according to Reuters.
Joint exploration operations are to take place in the Kara Sea, the body of water between the northern coast of Russia and the Novaya Zemlya island chain, as well as in the deep waters of the Black Sea, in the south of Russia.
Rosneft has calculated reserves in the Kara Sea’s East-Prinovozemelsky field at 35.8 billion barrels of oil and 10.3 trillion cubic meters of natural gas, the Washington Post reports.
The Russian government holds a majority stake in Rosneft, the Post says. It became Russia's largest oil company after acquiring the assets of Yukos, which was broken up in 2005 and its former chief Mikhail Khodorkovsky imprisoned.