Passive margin. Three craton-margin embayed basins--Kutch, Cambay, and Narmada--in the northern part of the shelf, are filled predominantly with clastic sediments. These basins occupy grabens bounded by faults diverging seaward. The grabens were formed by three rift systems along major Precambrian tectonic trends. Kutch Basin was formed in the Early Jurassic, followed by Cambay Basin in Early Cretaceous time, and the Narmada in the Late Cretaceous. Rifting occurred at successive stages during the northward migration of the Indian Plate. Rift basins opened up successively as a result of the counterclockwise drift of the Indian craton. Bombay offshore and Cambay are two major oil-producing basins in the western margin. These basins are characterized by high geothermal gradients attributed to the shallowness of the mantle in this region. Oil has not been found in Kutch Basin.--Modified journal abstract.