This has given Western companies access to new opportunities, such as Exxon's recent deal with Russian oil giant OAO Rosneft to explore the Black Sea.

WSJ: Exxon Struggles to Find Oil

Big onshore fields in the world's most prolific hydrocarbon provinces are increasingly the preserve of national oil companies, state-owned behemoths like Saudi Aramco and Russia's OAO Rosneft and OAO Gazprom.

WSJ: Big Oil Companies Are Shifting Their Focus Back to the West

Much of the money comes from a group of corporate sponsors and investors that includes state-owned lender OAO Sberbank, state-owned oil giant OAO Rosneft and oligarch Vladimir Potanin's holding company Interros.

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