An industrial semibatch nylon 6 reactor has been optimized using a one-variable (at a time) search technique. The vapor release rate from the reactor and the final monomer conversion have been constrained to lie very close to the values currently present. The degree of polymerization of the product is, similarly, constrained to lie at a value of 152. The optimal pressure histories for two values of the jacket fluid temperature, T-j, have been evaluated using two objective functions, I-1 and I-3, namely, the total reaction time (I-1 = t(f)) and the concentration of the cyclic dimer (I-3 = [C-2](f)) in the product. It is observed that as T-j is increased from 270 to 280 degrees C, I-1 improves while I-3 worsens simultaneously. This suggests that these two optimal points lie on the Pareto set for the two-objective function problem.