The inhibition of mild steel corrosion in 0.5 M H2SO4 by simple amines (cyclohexylamine, pyridine, triethylamine) was investigated by dc polarization, electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS). The results indicate a strong dependence of the inhibition performance on the nature of the metal surface, in addition to the structural effects of amines. Inhibition is accomplished by amine adsorption on the metal surface without detectable changes in the chemistry of corrosion. Adsorption is predominantly chemisorptive in the active region and by hydrogen bond formation in the passive region. Amine molecules with delocalized pi electrons or high electron densities at their nitrogen atoms are effective inhibitors in the active region. The effectiveness for corrosion control in the passive region, however, is proportional to the number of NH linkages in the amine molecules.