Carbon dioxide management issues among many include handling processing compression and transportation. In the Oil & Gas industry these tasks typically involve large amounts of liquid water which will provide the electrolyte necessary for the corrosion process to take place. The consequent damages can vary from general corrosion to localized pitting attack. However the unique feature of CO2 corrosion of promoting deposition of iron carbonate (FeCO3) layer under suitable conditions may provide some level of protection. This layer can suppress the corrosion rate to an acceptable engineering limit. The current works undertake study of the corrosion behavior of mild steel in high partial pressure CO2 system which covers all three states; gas liquid and supercritical CO2. Applications of electrochemical techniques outperform weight loss measurement which only generalized the overall corrosion rates with time. The transient behaviors of the corrosion processes are revealed with extreme initial corrosion rate (32mm/yr) during film free condition to very low corrosion rate (0.1mm/yr) during film forming condition. This presence of a protective film is indicated by a shift in the open circuit potential of about 200mV more positive imitating a passive film likes behavior.