"We are delighted to confirm the largest-ever gas discovery by PTTEP," chief executive Phongsthorn Thavisin said, adding that the discovery strengthened the company's investment base in Malaysia.

The discovery is based on the appraisal of Lang Lebah-2 in the Sarawak SK 410B project, about 90 km (55.92 miles) offshore of the Malaysian state of Sarawak.

The announcement comes after the PTTEP acquired a 20% stake in Oman's Block 61 form British oil major BP Plc for $2.6 billion this month.

The appraisal drilled to a total depth of 4,320 metres with proven over 600 metres of net gas pay, PTTEP said, adding that well test showed a flow rate of 50 million cubic feet of gas per day.

A PTTEP subsidiary operates the project, holding a 42.5% stake along with Kuwait's KUFPEC and Petronas Carigali Sdn. Bhd, holding 42.5% and 15%, respectively.

(Reporting by Chayut Setboonsarng; Editing by Martin Petty)