The oxidation of hydrogenated 2-ethyl-anthraquinone in a continuous stirred tank reactor has been studied. This reaction is considered usually as slow or moderately fast and both diffusion and reaction affect the overall rate. The interesting mass-transfer parameters : mass-transfer coefficient k(L) and the correlation constants of the volumetric mass-transfer coefficient k(L)a, were estimated with a steady-state model consisting of a set of implicit non-linear, algebraic equations. Ten screening experiments and five sequentially designed experiments based on the D-optimality criterion were carried out. The agitation speed, superficial gas velocity and the pressure served as the control variables. The response monitored was the concentration of unreacted hydroquinone in the effluent stream. The agreement between model prediction and experimental data was good. As all the model parameters could not be identified satisfactorily as such, some parameter transformations were necessary to achieve more accurate parameters. For satisfactory identification of the parameters, their sensitivities were viewed by plotting R(2) contours of the fit with pairwise parameter intervals. The reaction-diffusion model was simplified by assuming pseudo first-order kinetics for the reaction taking place in the film. The estimated values of mass-transfer quantities correlate well with results published earlier.