The Auger spectra of several carefully prepared Al-Cu alloys have been analysed in the light of recent models regarding the back-scattering factor and the escape depth. A detailed analysis of other bimetallic alloys taken from the literature is also presented. The analysis indicates that the choice of back-scattering factor model does not have much influence on the matrix factor and composition calculation. The calculated values of the compositional dependence of the matrix factor using different models of the back-scattering factor and escape depth do not agree with the experimental values throughout the whole concentration range. However, such a discrepancy in the matrix factor is dwarfed by the determination of the alloy composition, and it is seen that for lower concentrations of the component having a smaller atomic number in the alloy, the calculated value using Seah and Dench's (SD) model of the escape depth and that using only the density correction are better. For higher concentrations, the Tokutaka, Nishimori and Hayashi (TNH) model fits the experimental value well. For an Al-Cu alloy the three Cu peaks, very near to each other, have been combined with an Al peak to probe the compositional change with depth. A change of 0.1 nm in depth does not produce a significant change in the composition.