Recent experiments in the Gulf of Mexico have yielded a wealth of information on the environmental conditions and geoacoustic response of a uniform sand stratum immediately beneath the seafloor. A comparison of p-wave velocities measured at low (125 Hz) and high (11–50 kHz) frequencies in this layer indicates that there is a significant amount of velocity dispersion that occurs in the interval between these extremes. This narrow-band dispersion, which is not consistent with the often-used assumption of a nearly constant-Q model, is in accordance with the predictions of the Biot theory. It results from viscous damping in the fluid as it moves relative to the skeletal frame. Other recent field data that support this conclusion are presented.