In this study, critical pitting temperature (CPT) of G3 alloy under high temperature and high H₂S/CO₂ pressure environments was assessed using potentiostatic and electrochemical impedance spectroscopy (EIS) techniques. EIS measurements were carried at anodic potential of 150 mV vs. E_corr and the results were compared with those of potentiostatic polarisation. The results revealed that the CPT of G3 Alloy under high temperature and high H₂S/CO₂ pressure environments was 58.5 _oC in potentiostatic method and between 50-60 _oC in EIS method. Both potentiostatic polarization and EIS methods give an almost identical CPT value.