A combined experiments and mathematical modelling were carried out to study the kinetics of nonylphenol ethoxylation. Experiments were carried out in a well-stirred reactor used in an industrial research laboratory. The governing equations of the kinetic model were solved using Mathematica (2009). Results were validated against published kinetic data. The experiments and kinetics modelling were extended to account the presence of nitrogen in the vapour phase for a potassium hydroxide catalyzed ethoxylation of nonylphenol in a well-stirred reactor. The modelling results were successfully validated against the experimental data. This model has been successfully used (Chiu et al., 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. (C) 2009 Elsevier Ltd. All rights reserved.