New production concepts in the chemical industry like modular plants react flexible to the challenges of uncertain boundary conditions. The real option approach assesses these criteria of uncertainty and flexibility simultaneously. This article gives an introduction into real option analysis and applies this approach to modular chemical plants. Results of a case study show the additional flexibility value as a function of the degree of uncertainty. In this case the advantageousness of different production concepts can be reversed. Finally sensitivity analyses shed light onto the driving parameters of the developed assessment model.