Project Final Report-DE-FC26-06NT43067-The mass of carbon held in sediments below the sea-floor is a significant element of the earth’s carbon cycle. The amount currently in place may be large enough to implicate methane hydrates in global warming events in the geological past and also to raise the prospect of a vast energy resource. However, estimates of this mass and the rate at which it can accumulate in or dissipate from sediments vary widely. One reason for this is the difficulty in ascertaining the form and spatial distribution of methane within the HSZ. This project will quantitatively describe the manner in which methane is transported within the HSZ and will seek to prove or disprove the following hypothesis: The coupling among geomechanics, the dynamics of gas/water interfaces, and the phase behavior of gas/brine/hydrate systems, make co-existence of free gas and hydrate in the HSZ inevitable.