The addition of short chain polyethylene glycols (PEGs) activated Chromobacterium viscosum lipase in AOT reverse micelles. In this study, it was assumed that when AOT reverse micelles contained PEG molecules, native and activated lipases contributed to the reaction according to their weight fraction in the system. The fractions of individual lipases and their specific activities were estimated by using kinetics parameters determined by previous kinetic models. The maximum specific activity of PEG-activated lipase appeared to be 2.7 times higher than that of native lipase. The predicted weighted-average activity agreed well with experimental data. The results showed that the previous kinetic models could be used to estimate the fraction of lipase activated by PEG molecules and their specific activity. (C) 2004 Society of Chemical Industry.