The appointments were announced in a statement issued after a Total board meeting. The statement said Desmarest would keep his new position until the end of 2015, whereafter the roles of CEO and chairman would be combined again.
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Pouyanne had a key role in merging Total's loss-making refining and petrochemical units in recent years, and also had senior roles at the group's exploration units in Angola and Qatar.
A graduate of France's elite Polytechnique and Mines engineering colleges, he was also an adviser in ministerial offices under previous conservative governments.