"We don't comment on speculation -- and there has been a lot of speculation -- but I will say this: Opel is not for sale," Akerson said at a news conference on Wednesday when asked about Opel's future.
Akerson was speaking at a GM plant to officially launch labor talks with the United Auto Workers union.
Speculation about Opel's future began in early June with reports by German media the European unit could be sold and that possible buyers included Chinese automakers or Volkswagen <VOWG_p.DE>.
Opel Chairman Nick Reilly said on June 30 that GM was "very satisfied" with Opel's progress, but failed to quash rumors GM was mulling a sale.
However, Opel remains a high-cost player in a low-growth region, in a segment dogged by cutthroat competition, leading to speculation of a sale or labor concessions by its workers.
Earlier this month, when criticizing VW CEO Martin Winterkorn for speculating on Opel's fate, GM failed to address specifically whether Opel was for sale.
German government leaders and Opel union officials have been frustrated by GM's refusal to address the rumors directly.
Opel officials were not immediately available to comment on Wednesday.