Most design or retrofit focuses on cost savings as the objective. We treat instead two simultaneous noncompatible objectives : cost and flexibility, in the design of a process that must be controllable under future uncertainties. By use of an index of operational flexibility and Pareto decision theory, a biobjective problem is solved that yields an economical and flexible design. Evaluation of a sequence of possible critical input variables can be carried out based on a sensitivity analysis of the Lebesque measure of the feasible region of operation with respect to the input, control, and design variables.