Marine 3-D acquisition techniques commonly use multiple sources and streamers towed behind the seismic vessel. The full potential of modern 3-D processing can only be realized if accurate positioning of these sources and streamers is achieved. A multipath acoustic ranging technique has been used to solve this positioning problem. Ranges are determined from a network of measurements of the propagation times for ultrasonic waves traveling between pairs of transducers located at strategic points on the hull of the vessel, the source subarrays, and the streamers. The system falls naturally into two subsystems: a front-end subsystem and a streamer shape-positioning subsystem. The front-end subsystem described is used to determine the position of the source subarrays and the streamer tow points. This subsystem has been employed on surveys in the North Sea, and examples of the measurements are given. Factors such as the ship's velocity and heading affect the translation of the timing measurements to ranges. Applying the technique of variation of coordinates to these distances, all the positions in the front-end system have been calculated giving real-time displays which are updated every shotpoint. From the results, the positioning is estimated to have an accuracy of + or -1.5 m cross-course and + or -0.5 m along-course relative to the ship's navigation reference points.