A new method of estimating the mixing time in industrial Rushton turbine-agitated reactors under aerated conditions is presented -called the analogy mixing-time model. It is based on the hypothesis of the analogy at the same turbine agitation speed between the mixing time in single liquid phase and that in two gas-liquid phases. This assumption is validated for production tanks equipped with two. three and four Rushton impellers. Furthermore. it is demonstrated that the internal geometry of the reactor, the number of impellers, the distance between impellers, etc., and the degree of homogeneity do not affect the model. Only the location at which the pulse is injected is found to influence the sensitivity coefficient. This result thus makes the analogy mixing-time model very useful in determining agitation parameters in production stirred reactor. The physical mechanisms behind the model are clarified with general gas-liquid flow patterns described in the literature. The study is completed by the description of the formation of concentration gradients in one of the reactors studied (12 m 3 reactor). The effects of aeration on gradient formation are clarified with both bulk and impeller region injections. The results obtained are used for the design of a scaled-down reactor that mimics the environment created in the tank,