A detailed AVO analysis was performed on data from the Blake Outer Ridge to evaluate the origin of the bottom simulating reflector. We could clearly discriminate the effects of the two proposed models and showed that the BSR best fits a model of impedance contrasts between sediments containing a substantial amount of hydrate overlaying sediments containing free gas. A transition from hydrate to brine sediments is not consistent with the AVO amplitude responses and impedance contrasts. Assuming a reflection coefficient of 0.2 at the seafloor, the P impedance contrast at the BSR could be determined to -0.4. It has the same magnitude but opposite polarity to the seafloor impedance contrast. The resulting S impedance contrast of 0.8-1.2 at the BSR is two to three times larger than the seafloor S impedance contrast of the same polarity. A horizontal reflector below the BSR might be a ``flat'' spot which separates the free gas trapped below the BSR from deeper sediments saturated with water. However, this flat spot interpretation is so far inconclusive. A prestack migration impedance inversion might clarify the flat spot properties.