Freshfields Bruckhaus Deringer and Herbert Smith Freehills have advised as Thailand oil and gas giant PTT Exploration and Production (PTTEP) has bought Hess' Thailand assets for $1bn.

The company, which is the exploration and production affiliate of Thailand's state-owned energy company PTT, said in a statement today it would acquire 100% equity stakes of Hess subsidiaries, which own minority stakes in two Thai oil and gas blocks.

After the transactions have both closed in May, the company said its production volume will be increased approximately 17,000 barrels of oil equivalent per day.

Freshfields was advising Hess Corporate on the deal, led by Singapore partner Gavin MacLaren who heads the firm's Asia-Pacific energy and natural resources practice.

He also advised Hess in December on the sale of its Indonesian assets to PTTEP and Indonesian state-owned oil company PT Pertamina for $1.3bn.

Acting for PTTEP was Herbert Smith Freehills, with Seoul managing partner Lewis McDonald heading up.

Earlier this year the firm's London energy team also advised PTTEP Canada – a subsidiary of PTTEP – on the division of its interests in the Kai Kos Dehseh (KKD) oil sands project in Alberta Canada, with statoil.

PTTEP has invested in over 40 petroleum exploration and production projects in Southeast Asia, Middle East, Africa, Australia, North America and, now also in the South America continent.

The decision to boost its investment in projects is understood to reflect rising demand for oil and gas in South East Asia and a subsequent pressure on oil and gas companies to meet higher production quotas.

Related: Bakers and HSF among advisers as Asia energy giants invest in Australian wind farms