The proposed New Ship Lock for the Mississippi River-Gulf Outlet, Louisiana, will be 150 ft wide by 1290 ft long (pintle to pintle) and will have lifts varying from 1.0 to 18.4 ft as well as reverse heads up to 3.0 ft. Two sets of miter gates are planned to care for reverse heads. Since the proposed lock is some 40 ft wider than any locks previously designed in the United States and will be used by both ship and barge traffic and will be subjected to reverse head conditions, a hydraulic model investigation of the filling and emptying system was required. Results of tests of the hydraulic system for the proposed lock in a 1:25-scale model are presented in this report. The original intake and outlet designs which must perform as both intakes and outlets were investigated and found to be satisfactory. Tests of 20 sidewall port manifold arrangements resulted in the recommendation of the type 15 sidewall port manifold arrangement. The type 15 (recommended) design sidewall port system as developed is considered optimum for barge tows and will be satisfactory for ships with the proper clearance provided between the bottom of the ships and floor of the lock chamber. For the culvert size and sidewall port system selected, the optimum elements were developed from model tests.