Through the use of Monte Carlo simulations we study the effect of adsorption-induced segregation. From the bulk composition, degree of dispersion and the partial pressure of the gas phase species we calculate the surface composition of bimetallic alloys. We show that both segregation and adsorption are well-described within the method. It is shown that adsorption of CO and O(2), on a PtRu alloy increases the concentration of Ru in the surface. Furthermore we present a database of CO adsorption energies collected from the literature. (C) 2002 Elsevier Science B.V. All rights reserved.