Thai Oil, the country's top oil refiner, said on Friday it was interested in acquiring Esso (Thailand), a unit of Exxon Mobil, as part of its expansion drive.

"I admit that we are studying the possibility of buying Esso," Chief Executive Surong Bulakul told Reuters. "There's no specific timeframe when the study will be done because we have to look at several details."

This is the first time Thai Oil, part of Thailand's top energy firm, PTT, has confirmed market rumors about a possible acquisition.
Surong said the study would also involve the impact on shareholders, including the Finance Ministry, which owns 7.33% of Esso. Exxon owns 65.43% of the Thai unit.

Esso, valued at $1.18 billion on the Thai bourse, operates a refinery with capacity of 177,000 barrels per day, accounting for 16% of Thailand's total.

Esso listed shares on the Thai bourse in May 2008 with an IPO price of 10 baht.

The takeover speculation has pushed the share price up 33% over the past month, when the main index has risen just 0.7%. On Friday, Esso shares closed down nearly 1% at 10.30 baht, while the broader index was 0.09% higher.

Thai Oil, valued at $5.4 billion, has a refining capacity of 275,000 barrels a day of crude oil and other feedstocks, representing about 25% of Thailand's total.

Last month, PTT announced a plan to merge two affiliates, PTT Chemical and PTT Aromatics and Refining, as part of a consolidation of its downstream business.

PTT has stakes in five of the seven refineries in Thailand.