The Tengiz field in Kazakhstan holds 6 billion to 9 billion barrels of recoverable oil.

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ExxonMobil's problem may stem from Williams' aggressive efforts to get at the Tengiz oil.

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In 1993, Chevron signed a 40-year pact with Kazakstan to exploit the Tengiz fields.

CNN: THE BIG OIL SHOCK

Because Tengiz oil is so high in corrosive sulfur compounds, it must be partially refined before going through the pipeline.

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The government has also been quietly offering to sell part of its stake in the consortium operating the Tengiz field.

ECONOMIST: Kazakhstan

The Tengiz problem is a mere puddle next to the troubles at Kashagan in the remote North Caspian Sea, the world's largest oilfield discovery in the last three decades.

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The city is also host to the world's largest gas-stimulation project in development: 240 million cubic feet of Tengiz natural gas is injected daily into the reservoirs to loosen up oil and boost well pressure.

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