Table 1 lists several estimates of natural gas, in hydrate form, in the geosphere’s GH stability zone (i. e., the P and T regime within which hydrates are stable). The maxi­mum value (3.053 x 10,8 m3 STP of CH.) of Trofimuk et al. [195] is based on the assumption of GH occurrence wherever a satisfactory P-T regime exists, while the minimum value (2 x 1014 m3 STP) of Soloviev [180] accounts for limiting factors such as CH4 availability, limited organic matter, porosity, regional thermal history, etc.

The Klauda and Sandler [80] estimate in Table 1 has received significant atten­tion, as it is based on a state-of-the-art model that explains most known GH occur­rences and offers plausible reasons for discrepancies from its predictions.

Even the most conservative estimates suggest enormous amounts of gas in hydrated form, the magnitude of which can be appreciated by comparing them to the current rate of 1012 m3 STP of gas-equivalent annual energy consumption in the United States. All estimates are comparatively large relative to estimates of the conventional gas reserves of 1.5 x 1014 m3 of methane [155]. Kvenvolden [97] indi­cated that his estimate of 1.8 x 1016 m3 of CH4 in hydrates may surpass the recover­able conventional CH4 by two orders of magnitude, or be a factor of 2 larger than the CH4 equivalent of the total of all fossil fuel deposits.