Exxon Mobil (XOM.N: Quote, Profile, Research, Stock Buzz) has sold a 20 percent stake in two offshore exploration blocks in Indonesia to Malaysia's state oil firm Petronas [PETR.UL], an official at the country's energy watchdog said on Wednesday.

Exxon Mobil is the operator of the offshore Surumana and Mandar blocks in the Makassar Strait.

Exxon Mobil wants to share the burden of the exploration, said the official at the energy watchdog, known as BPMIGAS.

The official, who declined to be identified, did not give any financial details.

Maman Budiman, a senior vice president at Exxon Mobil Indonesia, confirmed the firm was cooperating with Petronas over the blocks, but declined to elaborate.

Exxon holds an 80 percent stake now in both Surumana and Mandar blocks. We are still conducting exploration in both deepwater blocks, Budiman said.

Indonesia awarded Exxon Mobil the exploration rights in Surumana block in 2006 and the Mandar block in 2007.

Indonesia has turned into a net importer of crude oil in recent years as production has slumped after a failure to tap new fields fast enough.

The country has been offering new exploration rights and financial incentives for oil fields in a bid to stem a steady decline in production.

(Reporting by Muklis Ali; Editing by Ed Davies)