The consistent line from Rex Tillerson was that Exxon had deep enough pockets to invest through the cycle after its acquisition of XTO in 2010.

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Rex Tillerson, Chairman and CEO of Exxon Mobil Corp.

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His successor, Rex Tillerson, has overseen a gradual opening up.

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Last year Rex Tillerson, chief executive of Exxon Mobil, took a step back from stock buybacks and allowed IBM to replace his oil behemoth as the U.S. stock repurchase leader.

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Under Rex Tillerson, the current boss, policy changed to support for a carbon tax, a proposal so much more radical than the cap-and-trade emissions bills on offer that critics suspected it of being an intentional distraction.

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Instead of cutting his teeth in the oilfields like Exxon Mobil CEO Rex Tillerson or wildcatting billionaire Harold Hamm, Watson studied agricultural economics and started his oil career as a financial analyst, not a roughneck.

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