In this work, computational studies on some imidazole derivatives which behave as corrosion inhibitors at various levels for iron in hydrochloric acid were carried out in gaseous and aqueous phases using semiemprical methods such as MINDO/3, MNDO, PM3 and AM1. Possible correlations between experimentally obtained inhibition efficiencies and calculated highest occupied molecular energy level (E-HOMO), lowest unoccupied molecular energy level (E-LUMO) and the differences between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies (E-LUMO - E-HOMO) were studied. Correlation between inhibition efficiencies and total charges (Z) of molecules, were also investigated. Regression analysis were performed on inhibition efficiencies (P), (E-HOMO) and (E-LUMO) energies of the studied molecules. (C) 2002 Elsevier Science B.V. All rights reserved.