The corrosion inhibition of carbon steel in HCl and H2SO4 solutions in the presence of some benzimidazole derivatives such as benzimidazole (BI), 2-methylbenzimidazole (2-CH3-BI) and 2-mercaptobenzimidazole (2-SH-BI) was investigated using potentiodynamic polarization technique. Results obtained showed that the benzimidazole derivatives retard both the cathodic and anodic reactions in both acidic media, by virtue of adsorption on the carbon steel surface. This adsorption obeyed Langmuir's adsorption isotherm. In the both media, 2-SH-BI showed the highest efficiency while the lowest efficiency was observed for BI. The comparative analysis of the inhibitor adsorption in both the media, as well as, the synergistic effect of bromide ions (Br-) in H2SO4 solution suggests that the physical adsorption of the cationic form of BI and 2-CH3-BI occurs, while 2-SH-BI is adsorbed chemically. (C) 2010 Elsevier B.V. All rights reserved.