Exxon Mobil Corp. named Dan Ammann as head of its upstream oil and gas business, putting its low carbon president in charge of its most profitable division.

Exxon Mobil said on Tuesday that Dan Ammann, former president of General Motors , will take over its largest and most profitable business early next year.

The head of Exxon Mobil’s massive exploration and production arm is retiring after more than three decades with the energy giant and will be replaced by a former General Motors executive.