Statistical group transfer copolymerization (GTP) of acrylates with methacrylates have been performed for four binary systems using 1-methoxy-2-methyl-1-trimethylsilyloxypropene (initiator) and tetrabutylammonium bibenzoate (catalyst) in tetrahydrofuran solution. The copolymer compositions were determined by H-1 n.m.r. spectroscopy and the results evaluated by the extended Kelen-Tudos method. The monomer pairs concerned are (1) ethyl acrylate (EA) and methyl methacrylate (MMA), (2) methyl acrylate (MA) and ethyl methacrylate (EMA), (3) MA and butyl methacrylate (BMA) and (4) MA and iso butyl methacrylate (i-BMA). The reactivity ratios were found to be gamma(EA) = 14.15, gamma(MMA) = 0 01, gamma(MA) = 14.41, gamma(EMA) = 0 01, gamma(MA) 13.96, gamma(BMA) = 0.23, gamma(MA) = 8.66 and gamma(iBMA) = 0.08 respectively. Statistical anionic copolymerizations were also carried out for two monomer pairs to compare with the results for GTP. The reactivity ratios are gamma(EA) = 9.67, gamma(MMA) = 0.11 gamma(MA) = 3.51 and gamma(EMA) = 0 20. It was found that acrylate is much more reactive than methacrylate; the reactivity ratios are quite different from unity and show a high similarity in GTP and anionic polymerization.