File photo of core samples of the Bazhenov formation, the world's largest shale oil resource, obtained by exploratory drilling in Russia's oil hartland in West Siberia, at a warehouse of the Tyumen ... more 
File photo of core samples of the Bazhenov formation, the world's largest shale oil resource, obtained by exploratory drilling in Russia's oil hartland in West Siberia, at a warehouse of the Tyumen Oil Research Centre in Tyumen February 12, 2013. Russia is introducing tax breaks to encourage the extraction of tight oil, trapped in non-porous rock, which will take effect from September 1, 2013, ensuring as much as $21 more per barrel stays in the pocket of exploration companies if oil prices average $100, experts say. State-controlled oil major Rosneft, which lobbied for the tax concessions, has teamed up with ExxonMobil Corp of the United States to develop the vast Bazhenov tight oil play in Siberia that was discovered in the Soviet era but remains largely untapped. Bazhenov, measuring 2,000 km by 1,700 km, could hold as much as 1 trillion barrels of oil, according to one estimate, four times the reserves of Saudi Arabia and enough to meet current global demand for 30 years. REUTERS/Maxim Shemetov/Files (RUSSIA - Tags: ENERGY BUSINESS SCIENCE TECHNOLOGY ENVIRONMENT) less 
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Reuters | Photo By MAXIM SHEMETOV / REUTERS
Fri, Aug 30, 2013 9:34 AM EDT