Two internationally-partnered research well programs, in 1998 and 2002, studied the Mallik gas hydrate accumulation in the Mackenzie Delta, Canada. Gas hydrate bearing intervals were cored, logged and production tested thus establishing Mallik as an excellent site for testing geophysical imaging techniques. Here, we apply a model-based acoustic impedance inversion technique to 3D seismic reflection data acquired over the Mallik area to characterize gas hydrate occurrences and to help define their spatial extent away from well control. Sonic logs in Mallik research wells show that P-wave velocity of sediments increases with hydrate saturation, enough to produce detectable reflections for the lower two of three known gas hydrate zones. The inversion method converts these reflections into acoustic impedances from which velocity and hydrate saturation can be estimated. Acoustic impedance inversion results indicate that the deepest gas hydrate zone covers an area of approximately 900,000 m2. With some assumptions on the lateral continuity of gas hydrate saturation, porosity and thickness measured at the wells, we estimate that this zone contains approximately 771x106 m3 of gas at standard atmospheric pressure. At a regional scale, results allowed the detection of a high-velocity area near the A-06 well, about 6 km south-east of 5L-38. We infer that the high velocity area corresponds to a gas hydrate accumulation. Logging data in A-06 indicate the presence of gas hydrates in this area and support our interpretation.