As part of a broad synthesis of geophysical data from passive continental margins bordering the South Atlantic, sediment sound-velocity functions have been derived for the Cape Basin off southwest Africa using velocity/travel time information gathered from multichannel seismic reflection profiles and sonobuoys. These functions allow more accurate sediment thickness calculations than similar functions previously derived for this region solely from sonobuoy results. However, a single basin-wide function is insufficient to predict thickness variations everywhere in the depocenter. Furthermore, sediment-velocity equations developed for the southern Cape Basin do not precisely define sediment thicknesses in the north, and vice versa. Equations appropriate to both regional and previously published crustal subdivisions of the basin produce the most consistent results relative to available well control, although possible associations between underlying crustal type and overlying sediment distribution on this passive margin remain unclear. Instead, the location of the Orange Cone deltaic accumulation south of the present course of the Orange River may be the principal factor responsible for separate southern and northern sediment-velocity provinces in the Cape Basin.