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A semiempirical calculation is outlined that allows analysis of experimental results for the apparent surface concentration of binary alloys, obtained by x-ray photoelectron spectroscopy, (XPS). A segregation profile giving the enrichment of the segregating element at and near the surface is obtained from the analysis. Using previously published data for Cu 17 Ni 83 ( 100) and Cu 17 Ni 83 ( 111 ), it is shown that copper segregation is not restricted to the first few layers, but instead extends significantly into the selvedge (near-surface) region. This occurrence is not explainable by the use of present ideal solution models. An extended ideal solution model is presented, in which the bond strengths vary gradually from top-layer values to bulk values. This model is consistent with the observed penetration of copper enrichment into the selvedge. The parameters describing the gradual change of bond strengths are determined via comparison of the results of the model with XPS data.