(Updates with confirmation, adds resignation details)
JAKARTA Aug 18 (Reuters) - The head of Indonesian state energy firm Pertamina will resign in October for personal reasons, and a director will be appointed on an interim basis until a replacement can be found, a company spokesman said on Monday.
Karen Agustiawan has served as president and CEO since February 2009, aggressively acquiring energy assets both at home and abroad to offset Pertamina's declining output.
"This was purely a personal decision. She felt this was the right time," said Pertamina spokesman Ali Mundakir, confirming earlier reports by local media.
"The Commissioners Board will appoint one of (Pertamina's directors) to act as CEO until a new CEO is appointed," Mundakir said, adding that Agustiawan's resignation and the selection of her replacement were subject to shareholder approval.
The new CEO will not be appointed until after president-elect Joko Widodo takes office on Oct. 20, Antara news reported.
Antara also reported that Agustiawan, who was Pertamina's first female CEO, was leaving Pertamina to take a teaching position at Harvard University.
Pertamina is one of Indonesia's most valuable state assets and sources of funding, and the process of choosing its leader are frequently embroiled in controversy and political feuds.
Over the next five years, the company plans to spend $61 billion, 83 percent of which will be on upstream development including mergers and acquisitions. (Reporting by Fergus Jensen and Wilda Asmarini; Editing by Muralikumar Anantharaman)