PTT Global Chemical Pcl fell as much as 3 percent on concerns about the possible impact of higher feedstock costs on the earnings of the country's biggest listed petrochemical firm.
PTT Global shares were down 2.6 percent at 56.25 baht ($1.77) at the midsession break of 0530 GMT, having hit 56 baht at one point. They have dropped 16 percent in May until Tuesday, underperforming the broader market's loss of 6.09 percent.
The majority of PTTGC's earnings are derived from gas-based olefin production, with feedstock supplied by parent company PTT Pcl. Uncertainties related to PTTGC's gas-based feedstock agreement with its parent PTT have worried investors.
"While there are currently no negotiations to adjust the net-back price agreement, it is said to be constantly under review ... Against our base-case earnings impact of a potential change in gas price, we believe the stock has been oversold," broker Kasikorn Securities said.
Kasikorn rates the stock at outperform, with a target price of 86 baht.
1240 (0540 GMT)
($1 = 31.74 baht) (Reporting by Viparat Jantraprap in Bangkok; Editing by Gopakumar Warrier)