Herbert Smith Freehills is advising Thai state-run PTT Exploration and Production Pcl. on a $1 billion purchase of Hess Corp.’s energy assets in the country.

PTTEP is paying cash for a 15 percent interest in an offshore natural gas project in the Gulf of Thailand, as well as a 35 percent stake in an onshore gas field in the northeast of the country. The deal for the offshore assets, which comprise two blocks, closed on Tuesday, while the onshore transaction is expected to close next month.

In a statement, PTTEP said the acquisition is part of the company’s strategy to continue boosting its holdings of producing assets and growing its reserves. In December, the company, along with Indonesian state-owned PT Pertamina, bought two Indonesian offshore oil and gas assets held by Hess Corp. Norton Rose Fulbright advised the acquirers on that transaction.

Seoul managing partner Lewis McDonald led the Herbert Smith Freehills team acting for PTTEP. Walkers served as the company’s Cayman Islands counsel.*

Freshfields Bruckhaus Deringer Singapore partner Gavin MacLaren is acting for Hess. Weerawong, Chinnavat & Peangpanor and Maples and Calder were Thai and Cayman Islands counsel, respectively.*

Email: tbrennan@alm.com.

*Updated, 4/23/14, 4:19 p.m.: This story has been updated to include Lewis McDonald as the Herbert Smith Freehills partner advising PTTEP, as well as Walkers as the company’s Cayman Islands counsel. Also, the roles of Weerawong, Chinnavat & Peangpanor and Maples and Calder as advisers to Hess were added as well.