Horizon Oil's (ASX:HZN) unit, Horizon Thailand Investments, will acquire a 7.5% interest in the Sinphuhorm gas field and a 60% interest in the Nam Phong gas field in Thailand from New York Stock Exchange-listed ExxonMobil for $30 million, according to a Monday filing with the Australian bourse.

The agreement includes contingent payments of up to $7.5 million over six years, subject to certain conditions.

The company will acquire 75% of ExxonMobil Exploration and Production Khorat (EMEPKI), with Malaysian-based independent energy firm Matahio Energy taking the remaining 25% and managing the Nam Phong field, the filing said.

The deal will be funded through an amended debt facility with Macquarie Group's (ASX:MQG) Macquarie Bank, providing up to $22 million, with an additional $10 million available post-completion of the acquisition, per the filing.

The acquisition provides access to 3.9 million barrels of oil equivalent of 2P proven and probable reserves at an estimated cost of $7.70 per boe, expected to deliver stable production of about 2,000 boe per day.

The deal is estimated to have a less than $10 million impact on Horizon's cash reserves, the filing said.