The goals of such analysis are to gain a better understanding of the response of seismic waves to geomechanical changes happening in the field and to improve our ability to discriminate between pressure and saturation signals using the time-lapse AVO response. Introduction A topic of great importance in time-lapse reservoir monitoring is whether we can separate production-induced changes due to saturation from those due to pressure. A second technique is to compare the time-lapse time-shifts [Hatchell and Bourne, 2005] with the time-lapse amplitudes. In this paper we look at both methods for pressure/fluid discrimination on 4D data volumes based on the combined use of time-lapse amplitudes with time-lapse depth-shifts as evaluated on true wide azimuth Mars 4D OBN data that captures both pre-production and post-production cases. Data acquisition and processing The deepwater (3000 ft WD) Mars Field is located in the central Gulf of Mexico, about 100 miles south of New Orleans.