Thirty-five epitaxial films of AlxGa1−xAs grown by LPE on GaAs substrates with 0.0<x<0.95 were examined by Auger electron spectroscopy. By averaging results obtained using the ratios of peak-to-peak heights for all three components obtained at both high and low energies and for several measurements, compositions reproducible to ±3% or better were obtained. While preferential sputtering of one component could affect the absolute accuracy, our results suggest that errors from this source were less than 2% at worst. The film compositions obtained in this manner were in excellent agreement with thermodynamic calculations based on growth conditions.