Exxon Mobil Corp. is pushing ahead with its plans to drill in Russia’s Arctic seas—its biggest opportunity to discover untapped deposits of oil and gas—even though deteriorating relations between Moscow and Washington have increased the risks. America’s biggest energy producer is set this summer to tap what it calls the University Prospect in the Arctic’s Kara Sea, a trove that could hold the equivalent of 9 billion barrels of oil—more than a third of Exxon’s proven reserves. That prize looks riskier as tensions increase between the West and Moscow over Russia’s . U.S. sanctions this week targeted Igor Sechin, a close associate of President Vladimir Putin and head of OAO , Exxon’s Kremlin-controlled partner in the Arctic. The sanctions didn’t extend to Rosneft itself. “All of the activities that we had originally planned for this year are under way,” David Rosenthal, Exxon’s vice president of investor relations, said Thursday […]