The electrochemical behavior of carbon steel was studied in near neutral buffered aqueous solutions saturated with mercaptoundecanoic acid (MUA) and dodecanethiol (DT) by using electrochemical techniques combined with X-ray photoelectron spectroscopy (XPS). MUA and DT adsorb on the Fe surface by cathodization in the potential range corresponding to the hydrogen evolution reaction by forming thiolate bonds. The presence of the adsorbate layer in contact with an extremely low amount of thiols in the neutral solutions hinders the hydrogen evolution reaction and prevents the formation of the iron oxides in a wide potential range. (C) 2009 Elsevier Ltd. All rights reserved.