A model for base-catalyzed ethoxylation of methanol in the semibatch reactor was established. The applied method for the parameter detn. was described. Simulations were carried out to find optimized operating conditions using the limiting operating conditions for max. possible selectivity (output). Substantial deviations between the simplified single reaction model (SRM) and the reaction network model (RNM) were shown to occur in the high sensitivity range (jacket temp. TM 85 Deg, SRM gave lower calcd. max. pressure and temp. than those predicted by RNM. These deviations were classified as dangerous from the point of safety engineering.