In 1973, the Philippine government, through the Philippine National Oil Company (PNOC), acquired Esso Philippines, Inc., including FilOil Refinery Corporation. Esso Philippines, Inc. was renamed Petrophil Corporation (Petrophil) and by 1974, Esso filling stations were rebranded as "Petron", a portmanteau of petroleum (PET) and research octane number (RON). Subsequently, Mobil (successor of Socony-Vacuum Oil Company) also sold its share in FilOil Refinery Corporation to PNOC. The oil refining and marketing units in PNOC, including FilOil Refinery Corporation, were merged into Petrophil Corporation.