Many shallow water, fine-grained sediments are almost acoustically impenetrable to the energy from high resolution, low energy continuous seismic profilers. It has been alleged that this anomalous acoustic behavior is the result of interstitial gas bubbles that produce reverberation within the sediment, but no analyses were made until recently to test this hypothesis. Determinations of the compressibility of sediments from acoustically impenetrable, or turbid, zones and from contiguous zones of good penetration in Chesapeake Bay showed that the acoustically turbid sediments are several orders of magnitude more compressible than acoustically clear sediments of very similar grain size. The increased compressibility is a result of the presence of interstitial gas bubbles. Other acoustically turbid zones are produced by buried shell beds, and do not show an increase in compressibility.