The effects of an exhaust plume and nozzle length on the flow organization of axisymmetric base flows have been studied experimentally at Mach numbers of 0.76 and 2.2 using particle image velocimetry. From the measured velocity data, the mean pressure field was computed. The application of different nozzle lengths resulted in flow cases in which the shear layer impinges on the model, on the flow downstream of the model, or intermittently on the model and on the flow. The results showed that, for intermediate nozzle lengths, the overall pressure level downstream of the base decreased in the transonic flow cases and increased in the supersonic flow cases, indicating an entrainment effect in transonic flow and a displacement effect in supersonic flow. An increase in nozzle length was found to lead to a higher local pressure at the nozzle exit, which seemed to result in more overexpanded plumes in the transonic flow cases and less underexpanded plumes in the supersonic flow cases.