The hydrodynamics of a continuous-flow stirred tank reactor (CFSTR) have been studied through RTD measurements, visual tracing, and CFD simulations, for an axial-flow and two radial-flow impellers (Mixel TT and Rushton and NS turbines), to investigate how the combination of impeller choice and operating conditions ( flow rates, agitator speed) affect the vessel hydrodynamics and flow nonideality. The portion of the total vessel volume being perfectly mixed decreases considerably as the vessel utilization is forced by decreasing the vessel retention time; at the same time the amount of feed bypassing/ short-circuiting increases, too, especially in the case of axial-flow impellers. Qualitative and quantitative results are obtained, leading to conclusions about the suitability of particular impeller-vessel configuration combinations.