The microemulsion (ME) and conventional emulsion (CE) copolymerizations of methyl methacrylate (MMA) with acrylonitrile (AN) are carried out at 70degreesC by employing sodium lauryl sulphate (SLS) and n-octanol (OA) as surfactant and cosurfactant, respectively, and potassium persulphate (KPS) as initiator. The copolymerization reactions are arrested at lower conversions, and the copolymers prepared are characterized by FTIR, NMR, TG/DTA, and GPC techniques. The reactivity ratios for microemulsion and conventional emulsion copolymerizations are evaluated by Fineman-Ross (F-R), Kelen-Tudos (K-T), and Mayo-Lewis (M-L) graphical methods. The K-T method yields the reactivity ratios of MMA (r(MMA)) and AN (r(AN)) as 2.03 +/- 0.02 and 0.10 +/- 0.02, and 1.97 +/- 0.02 and 0.13 +/- 0.02, respectively, for ME and CE copolymerization methods. The results are compared with the literature.