In terms of global distribution, oceanic hydrates constitute about 99% of the total GH resource [178], so that a 1% error in the ocean approximations could encompass the entire permafrost hydrate reserves [178]. Kvenvolden [98] compiled 89 hydrate sites shown in Fig. 1 [178]. At those locations, hydrates were:

1. Recovered as samples (23 locations, of which 3 in the permafrost and 20 in ocean environments).

2. Inferred from (a) Bottom Simulating Reflector (BSR) geophysical signatures (63 locations), (b) decrease in pore water chlorinity (11 locations), well logs (5 loca­tions), and slumps/pockmarks (5 locations).

3. Interpreted from geologic settings (6 locations).

A measure of the dearth of direct knowledge on hydrates compares this mea­ger list, which represents the entirety of the database of natural hydrates, to the huge body of information on conventional and unconventional oil and gas reservoirs [ 209 ] .

Given their relative abundance, marine GH occurrences will likely be the pri­mary targets for future R&D activities. However, given the favorable economics of conducting long-term field programs in the Arctic (as opposed to the deep water), it is expected that arctic R&D activities will also continue. Two countries, the United States and Japan, are making considerable R&D investments in the Arctic, under the reasoning that the information gained on the behavior of gas hydrate­bearing sand reservoirs can be readily transferred to the study of marine resources at a later date.

Fig. 1 I (63), recovered (23), and potential (5) hydrate locations in the world [98]