A companion article (Chen and Hu, 1993a) discussed a statistical theory that for a system consisting of two closed subsystems, the residence time density (RTD) functions of the two subsystems will bestatistically independent, ifa two-dimensional perfect mixing exists at the subsystem boundary. In this case, the overall RTD function is related to that for individualsubsystems through the convolution integral. This theory has been validated experimentally using two die-screw combinations.Based on this theory, a predictive RTD model for an intermeshing counterrotating twin-screw extruder has been developed. The screw in the longitudinal direction has been treated as C-chambers in series. The overall RTD of leakage flows has been calculated from the RTDs of these individual chambers and then converted into the RTD of the extruder. The predicted RTD has been tested against experimental results with success.