Sediment properties such as compressional speed and attenuation have been extracted using the modal dispersion of explosive signals in the Middle Atlantic Bight. Data collected during the Shelf Break PRIMER experiment are used to generate sediment sound speed profiles along various propagation paths. Compressional speeds are inverted using traveltime of modes 1 to 9 from 10 Hz to 225 Hz. Compressional attenuation is inverted using modal amplitude ratios. Gravity cores taken at the experimental site give direct mesurements of compressional speed and attenuation for comparison. A posteriori estimates of resolution are evaluated. Nonlinear inversion techniques based on a Genetic Algorithm and Levenberg–Marquardt methods are used. Methods for increasing the efficiency of the inversion algorithm are also investigated. [Work supported by ONR.]