Copolymer compositions and reactivity ratios for the radical copolymerization of styrene with acrylonitrile have been determined by x-ray photoelectron spectroscopy (XPS). The results obtained by this technique were confirmed by elemental as well as H-1-NMR(nuclear magnetic resonance) analysis. The monomer sequence distributions have also been calculated utilizing the monomer reactivity ratio values obtained by three different techniques viz., XPS, H-1-NMR, and elemental analysis. The agreement between the monomer sequence distributions in the copolymer chain by these methods is very satisfactory.