Methane hydrates are a naturally-occurring ice-like substance found in permafrost and in ocean sediments along continental shelves. Hydrates are sometimes the source of cold seeps—plumes which release methane gas into the marine environments, which may subsequently release the gas into the atmosphere. Methane hydrates and methane gas seeps are of particular interest both for their potential as an energy source and for their possible contribution to climate change. In an effort to improve location of hydrates using seismic surveys and echo-sounding technology, this research aims to describe the low-frequency (10 Hz to 10 kHz) acoustic behavior of hydrates in their solid and gas phases in natural and simulated marine environments. Work includes, but is not limited to, laboratory experiments on pressurized bubbly liquids, measurements of natural methane hydrate (structures I and II) sound speeds as a function of pressure, passive sensing of gas seeps, and finite element modeling and analysis of sediments and marine environments.