The electrochemical impedance spectroscopy (EIS) technique was Used to investigate the characteristics of the Surface film on the surface of carbon steel formed in static Simulated produced water saturated with supercritical carbon dioxide (SC-CO2). Electrical equivalent Circuits were proposed to describe the electrochemical behavior. The results showed that a protective surface film was observed on the surface of the pre-filmed samples. In general, the protective performance of the surface film was enhanced with the increase of the exposure time within the time period of 0-6 h. The surface film formed at a high temperature was more protective than that formed at a low temperature because the fast formation of the film at elevated temperatures and the surface film became more compact and continuous with the increase of the temperature. Results Of EIS were in good agreement with the weight-loss measurements. (C) 2004 Elsevier B.V. All rights reserved.