Vinyl acetate/butyl methacrylate (V/B) copolymers were prepared by free-radical solution polymerization in benzene. Compositions of the copolymers have been obtained from H-1-NMR spectroscopy. Kelen-Tudos (KT), the nonlinear error in variables method (EVM), and C-13 {H-1}-NMR spectra of the copolymers were utilized to calculate the comonomer reactivity ratios. The reactivity from different methods are r(V) = 0.06 +/- 0.02, r(B) = 26.34 +/- 8.49 (KT); r(V) = 0.06 +/- 0.01, r(B) = 26.88 +/- 3.59 (EVM); and r(V) = 0.06, r(B) = 18.20 (C-13-NMR spectroscopy). The microstructure in terms of V- and B-centered triad fractions was obtained using C-13 {H-1) -NMR spectra of copolymers. The copolymerization behavior of V/B copolymers as a function of conversion was also studied.