Petron Corp. (PCOR.PH) said Wednesday that its board has approved a plan to invest in U.S.-based ExxonMobil's (XOM) downstream oil business in Malaysia, an initial overseas foray for the Philippines' largest oil refiner by capacity and sales.

Petron has yet to finalize the size of the investment and the stake, it told the stock exchange.

Petron President Eric Recto told Dow Jones Newswires that the board has yet to decide whether to buy all or a portion of the stake that parent firm San Miguel Corp. (SMC.PH) owns in ExxonMobil, or take the remaining stake in the downstream business.

In August last year, Philippine conglomerate San Miguel reached an agreement to buy ExxonMobil's 65% stake in Malaysian oil refiner Esso for $610 million.

As part of the deal, San Miguel will get ExxonMobil's other downstream oil subsidiaries in Malaysia--ExxonMobil Malaysia Sdn. Bhd. and Exxon Mobil Borneo Sdn. Bhd.

-By Cris Larano, Dow Jones Newswires; 632-848-5051; cris.larano@dowjones.com