In order to better understand the occurrence and distribution of gas hydrates and their effects on acoustic and thermal measurements in ocean sediments, the authors have conducted a program of experimental research to study thermal conductivity and acoustic wave velocity in hydrates and sediments containing hydrate. The most significant result of these studies is that the formation of hydrate tends to cause a decrease in the thermal conductivity of a sediment. This is contrary to what might be expected on the basis of an analogy with the behavior of frozen sediment and implies that some thermal gradients assumed in earlier studies of in situ deposits of hydrate may be too small. Other results of the research based on measurements of acoustic wave velocity confirm that both pure water and water-bearing sediment are converted to a stiff elastic mass by the formation of a sufficient quantity of hydrate. This clearly establishes the potential for a sharp acoustic impedance contrast at the boundary of a region of sediment containing a significant quantity of hydrate.