Table 3. Calculated gas to water volumetric ratios and gas to gas hydrate volumetric ratios expected from dissociated Structure I gas hydrate containing only methane at conditions expected at the Blake Ridge (22-32 MPa), as compared to gas hydrate equilibrium pressures at 1 MPa.

Location	Site/Hole	Depth (mbsf)	Gas to water volume ratio	Gas to water volume ratio (chlorinity correction)	Chlorinity (mM)	Reference
Blake Ridge	533A	238	20		NA	Kvenvolden and Barnard, 1983
Middle America Trench	565	319	133	137	15	Kvenvolden et al., 1984
Offshore Costa Rica	568	404	30	36	92
	568	404	7	8	89
	570	192	4?		NA
	570	192	29	30	19
	570	192	29	30	19
	570	259-268	24-42		NA
	570	273	12		NA
Gulf of Mexico*	Green Canyon*	<5	152		NA	Davidson et al., 1986
	Green Canyon*	1-1.5	70	94	138	Brooks et al., 1984
	Green Canyon*		70	102	169
	Green Canyon-184*		70		NA	Brooks et al., 1989
	Green Canyon-204*	85		NA
	Green Canyon-234*		177		NA
	Garden Banks-388		68		NA
	Green Canyon-257		35		NA
	Green Canyon-320		66		NA
Offshore Peru	685A	165.6	100	111	51.4	Kvenvolden and Kastner, 1990
	688A	141	13	16	90.6
	688A	141	20	35	232.3
Cascadia, offshore Oregon	892D	18	70	81**	NA	Lorenson and Kastner, unpublished data
	892D	18	53	62**	NA

Notes: NA = not analyzed. * = structure II gas hydrate is likely though not confirmed; maximum gas to water ratio is 220, ** = calculated pore-water dilution of 14% from oxygen isotopic shift between gas hydrate water and pore water. Maximum values in nature are expected to be about 195-204. Values less than these reflect partial decomposition during core recovery. Values range from 4 to 177. A chlorinity correction made to some ratios using the nearest sediment pore-water concentration results in a revised range of 8-137.