We present chronocoulometry experiments and equilibrium Monte Carlo simulations for the electrosorption of Br and Cl on Ag(1 0 0) single-crystal electrode surfaces. Two different methods are used to calculate the long-range part of the adsorbate-adsorbate interactions. The first method is a truncated-sum approach, while the second is a mean-field-enhanced truncated-sum approach. To compare the two methods, the resulting isotherms are fit to experimental adsorption isotherms, assuming both a constant electrosorption valency gamma and also a coverage-dependent gamma. While a constant gamma fits the Br/Ag(1 0 0) well, a coverage-dependent or potential-dependent gamma is needed for Cl/Ag(1 0 0). (C) 2003 Elsevier B.V. All rights reserved.