Marine sediments under overburden pressure commonly develop elastic anisotropy, probably of the transverse type with a single vertical axis of symmetry. Surface measurements of sound interval velocity in such materials, as by wide angle reflection profiling, provide a value between the vertical and horizontal velocities, thus introducing errors when measured velocity is used in determining section thickness. Empirical regression equations from laboratory measurements allow estimation of in situ vertical or horizontal velocity when one or the other is known in marine calcareous (Vv, km/s=0.18+0.89 Vh) and silt-clay (Vv, km/s=0.25+0.83 Vh) sediments and sedimentary rocks. These equations allow determination of the maximum error caused by anisotropy in section thickness determinations.