Electrochemical impedance spectroscopy (EIS) and open circuit potential (OCP) measurements were used to study the ability of monocarboxylates to support the passivation of mild steel by dissolved oxygen in near neutral Solution. It was shown that the effectiveness of monocarboxylates depends oil their ability to form weakly soluble Fe(III) compounds and to adsorb oil the oxide covered surface. The inhibition effect can be improved by ail addition of a second inhibitor (c) 2008 Elsevier Ltd. All rights reserved.