Russian Prime Minister Vladimir Putin attended the Tuesday signing in the Black Sea resort of Sochi by Exxon Chief Executive Rex Tillerson and Russia's top energy official, Deputy Prime Minister Igor Sechin.
Exxon and Rosneft agreed to invest $3.2 billion developing East Prinovozemelsky Blocks 1, 2, and 3 in the Arctic Kara Sea and the Tuapse licensing block in the Black Sea.
Rosneft will own 66.7 percent and Exxon the rest of a joint venture to develop the blocks, which Exxon said were "among the most promising and least explored offshore areas globally, with high potential for liquids and gas."
Under the deal, Rosneft will tap the offshore expertise of Exxon to open up one of the last unconquered drilling frontiers, while diversifying further outside Russia by getting a piece of Exxon U.S. developments.
Rosneft said the Kara Sea blocks contained an estimated 36 billion barrels of recoverable oil resources. Total resources were estimated at 110 billion barrels of oil equivalent -- more than four times Exxon's proven worldwide reserves.
The Black Sea block was estimated to hold 9 billion barrels of oil reserves. First drilling was planned to start in 2015, with Exxon shouldering most of the costs.
Rosneft will be offered an equity interest in Exxon exploration projects in North America, including deepwater Gulf of Mexico and fields in Texas, as well as in other countries.