Operability analysis helps the process designer to consider process control issues quite early in the design process. This analysis should lead to the calculation of a measure which quantifies the operability of a design. Search for this measure has been an active area of research in the last two decades. Recently. Vinson and Georgakis proposed a steady-state operability index (OI) involving both the servo and regulatory aspects. Their primary focus was on linear systems. This paper demonstrates the utility of the OI approach to chemical reactors. Two designs of a nonlinear CSTR, with and without multiple steady states, are examined.