Abstract The corrosion by CO2/H2S in gas and petroleum production represents one of the most important areas of research, due to the necessity to evaluating the severity of corrosion and thus to decrease the risk of operation problems and in addition the decrease of effective costs of production. In Colombia, the researchers have been oriented to the study of CO2 corrosion, although in the country production can appear traces of H2S, which are potentially harmful for the materials of the hydrocarbon transporting pipelines. In this frst part, the steel in a multiphase system containing brine-CO2-H2S was evaluated. To carry out this research, the concentrations of CO2 and H2S and the hydrodynamics conditions present in the pipelines were simulated in an electrode rotating cylinder. In this geometry, the corro- sion rate was determined on steel AISI 1020, as well as, the mass transfer coeffcients and viscous layers of the representative species of the system; the morphology of corrosion products formed in these environments was also characterized. This study allowed concluding that the species related to CO2 (H2CO3), are those that infuence the mechanism of deterioration of steel AISI 1020. This behavior was strongly infuenced by the variation of the electrode speed, the temperature and pH.