A mathematical approach was taken in order to describe the pitting process in CO2 corrosion. The hypothesis established was based on a unidirectional pit model which involved nineteen species, one of them (Fe2+) being diffused from the bottom of the pit. Using numerical methods, a prediction of corrosion rates in the pit, concentrations of the species in the pit and pH profile were determined. The average corrosion pitting rate from CO2 was found by calculating the corrosion rate at various pit depths.