The cationic micelles of cetyltrimethylammonium bromide, cetyldibenzylammonium chloride and cetylpyridinium chloride stabilize the tetrahedral intermediate formed in the hydrolysis of carboxylic esters (e.g.p-nitrophenylbenzoate) to a greater extent, preferring a$$B_{Ac^2 } $$ mechnism, than the anionic intermediate formed in the hydrolysis ofm-nitrophenyl-N-N-diphenylphosphorodiamidate, which prefers aE_1cB mechanism. The co-operative index,n₁, calculated for these reactions is greater than 1 indicating that the substrate induced micellation is responsible for the observed catalysis. Based on the present kinetic model for a bimolecular reaction the fraction of substrate and nucleophile bound to the micelle have been calculated. The above results suggest that reaction occurs between the substrate solubilised into the micelle and the nucleophile residing at the Stern layer rather than at the micelle-water interface. The equilibrium constant, and critical micelle concentration evaluated using the present model are in agreement with the values obtained by using earlier models, suggesting a method of evaluating these parameters from kinetic data only.