A study of wave-mode conversion that occurs at the sea floor for downgoing seismic energy and a comparison with reflected conversions at a representative interface of Tertiary sediments is presented. To investigate if the presence of S-waves on the vertical component (and Pwave in horizontal) could be due to mode conversion close to the receivers, conversion for up-going seismic energy in the shallow sediments is also analyzed. It is concluded that: 1) most P-to-S conversion occurs as reflection at sediment interfaces, not at the sea-bottom, and 2) negligible mode-conversion (both P-to-S and StoP) occurs for the up-going seismic energy in the sediments and at the sea bottom.