In this study the pitting corrosion of steel API 5L grade B in saline solution and saturated with CO2 was evaluated, which are part of the fuids involved in oil production, the technique used for the study of this phenomenon was electrochemical noise (EN), to observe the possible effects on the electrode surface; The tests were performed at 25 and 45oC, varying the Cl- ions concentration between 500 and 24000 ppm. With the electrochemical noise test was detected the onset of pitting process. Tests were conducted at 2, 4, 6, 48, 480 hours, to ensure a reliable analysis of the phenomenon. Was concluded that the synergistic behavior between chlorides ions and CO2 content on carbon steel API 5L grade B immersed in saline solution, at different concentrations and saturated by bubbling with CO2, affects the microstructure of the material.