The flow-routing module of the Hydrologic Simulation Program-Fortran watershed model was calibrated for 31 reaches on the Delaware River and 5 of it principal tributaries. These calibrations primarily involved the development of discharge-storage volume relations for the defined reaches. Daily discharge records for stream-gaging stations located at the upstream ends of the study reaches on the respective streams provided the primary hydrographic inputs for the routing models. Streamflow records for gaging stations at upstream locations and on other tributaries were used to estimate all other inflows for the 5-year calibration period, 1979-83. Root mean square errors of streamflows that were simulated for the downstream ends of gaged reaches ranged from 0.4 to 9.4 percent for the Delaware River, Lehigh River, Schuylkill River, and Brandywine Creek. Errors of 13 and 30 percent resulted from the streamflow simulations for the Lackawaxen and Neversink Rivers, respectively. Verification simulations for a 3-month period of extreme low flows on the Delaware River in 1966 resulted in overestimation of discharges for the Trenton, NJ, gaging station by approximately 50 percent on many days. Observed (recorded) streamflows at the Trenton gaging station during this time were exceptionally low, owing to comparatively large diversions of flow for public supplies, and into the Delaware and Raritan Canal. A flow-verification simulation for 3 months of the summer and fall of 1985, during which time minimum flows in the basin were comparable to those of 1966, resulted in a root mean square error of 3.3 percent for the Trenton gaging station. There was no diversion to the Delaware and Raritan Canal at the time. Simulated flows closely matched observed flows for upstream gaging stations on the Delaware River as well, thereby confirming the routing calibration for this stream. Information contained in this report can be used, with little modification, to develop routing modules for full-scale applications of the Hydrologic Simulation Program FORTRAN model to the watersheds of the studied streams.