A combined experiments and mathematical modelling were carried out to study the kinetics of nonylphenolethoxylation.Experiments were carried out in a well-stirred reactor used in an industrial research laboratory.The governing equations of the kinetic model were solve dusing Mathematica (2009). Results were validated against published kinetic data.The experiments and kinetics modelling were extended to account the presence of nitrogen in the vapourphase for a potassiumhydroxide catalyzed ethoxylation of nonylphenolinawell-stirred reactor.The modelling results were successfully validated against the experimental data.This model has been successfully used(Chiu etal.,2008) for optimizing the productivity of the existing alkoxylation reactors and can be used as a tool for the exploration and design of innovative new reactor systems.