U.S. sanctions against Russia prevented Exxon Mobil Corp. from pursuing ambitious plans to explore for oil north of Siberia. But the final blow, some experts said, may have been delivered by lower oil prices.

The Texas oil giant said in a regulatory filing late Wednesday that it would walk away from the joint venture with state-controlled PAO Rosneft to seek oil in the ice-choked waters of the Kara Sea, a hard-fought deal signed in 2012 by the company’s former chief executive, Rex Tillerson, now U.S. secretary of state.

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