A computer simulation model developed for studying the operating characteristics of alternative inland waterway transportation systems is described. The first part of the model (Towgen) processes information concerning commodity flows and waterway fleet characteristics to derive a list of tows that will move on the waterway under study. The second part of the model (Watsim) simulates the movement of these tows through the ports, locks, pools, and channel delay areas comprising the waterway system. Results of applying the model to a 10‐lock subsystem on the Illinois waterway and upper Mississippi River are give