The outlook is stable. Fitch has also affirmed TOP’s National Short-Term Rating at F1+(tha).

The rating upgrades reflect Fitch’s reassessment of the strategic importance of the petrochemical and refinery business to its parent, PTT Plc (PTT; AAA(tha)/stable), after business reorganisation over the past few years.

“The business, in which TOP is a major component, is more important than we previously anticipated,” Fitch said. The petrochemical and refinery business accounted for around 31 per cent of group revenue, while it was the second-largest contributor to group EBITDA at 28 per cent, following the exploration and production business with 36 per cent in 2018.