The report said an unattributed statement faxed to the Thai press yesterday claimed that Shell had been secretly negotiating to sell its 75% stake in the S-1 concession, which includes Sirikit, Thailand's largest onshore oilfield, located about 400km north of Bangkok.

The fax claimed that the planned sale by Shell had been a cause of concern for both government agencies and Thai Shell employees because there was a chance that any new operator would be less capable at operating the complex oilfield.

The field was the first major onshore oil discovery in Thailand but currently only yields about 20,000bopd. With production declining, Shell has applied a pressure-maintenance scheme to sustain oil output from the field for the last few years.

A Thai Shell spokeswoman told The Nation that there had been no decision to sell its stakes in the S-1 concession. However, Shell regularly reviewed its assets and the S-1 field was among those that would be reviewed.

The Sirikit oilfield began production in 1983 and is located in Kamphaeng Phet province.