Recent papers [W. Piasecki, Langmuir 22 (2006) 6761; P. Zarzycki, Langmuir 22 (2006) 11234; P. Zarzycki, J. Colloid Interface Sci. 306 (2007) 328] showed that the distinction between surface heterogeneity and effects of electrostatic interactions becomes problematic for metal oxide/electrolyte systems. This observation suggests that both mentioned factors can be combined into one ("effective" energy). Hence, the effective adsorption energy distribution function (EAEDF) with the Langmuir isotherm can be used in the framework of integral adsorption isotherm (IAI) instead of the classical adsorption energy distribution function (AEDF) with the Fowler-Guggenheim isotherm. The histogram method was used to obtain the effective distributions from the grand canonical Monte Carlo simulations of H+ ion adsorption. The new approach (IAI/EAEDF) gives a much better description of the heterogeneous metal oxide/electrolyte interface than IAI/AEDF. Moreover, reduced quantities are introduced in order to compare different metal oxide/electrolyte systems in a convenient way. (c) 2007 Elsevier Inc. All rights reserved.