The architecture of the western continental margin of India (WCMI) is likely to have been influenced in the geological past by several episodes of volcanic eruptions, rifting, and continental break-up. The WCMI is characterized by a wide shelf in the north (few hundreds of kilometers wide), which tapers down to just few kilometers towards the south. A detailed multibeam swath bathymetry study was made of a part of the wide flat shelf off Mumbai encountered at an approximate depth of 50 fathom (about 100 m) that holds one of the world’s richest offshore petroleum resources. The multibeam bathymetry images suggest that the western boundary of the Fifty-Fathom-Flat (FFF) coincides with the shelf break, with a fall much sharper than other places along the west coast. This break also coincides with the western extremity of the carbonate platform. The stratigraphic succession and petrology of the FFF bear strong resemblance to that of the Seychelles and Mascarene Plateau. The tectonic implications of such resemblance, and the possible reasons for the remarkably low bathymetric relief of the FFF is discussed