Systematic inversion techniques have been applied to travel time data from marine refraction profiles in the Pacific Ocean and are compared with the conventional uniform layer solutions for the same profiles. Extremal bounds are obtained on the possible velocity-depth distributions which fit the travel time data. Also a linearized inversion is used to construct suitable velocity-depth profiles together with a measure of their resolution. The velocity structures obtained indicate obtained indicate that layer 2 is a region of strong velocity gradients while layer 3 is relatively homogeneous, although it does show an increase in velocity with depth. The inverse schemes offer a useful alternative to fitting models containing uniform layers to the travel times from a seismic refraction profile.