Table 5. Composition of free gas collected in vacutainers from sediments at Sites 991 and 993.															

"Core, section"	Depth (mbsf)	O2 (ppmv)	N2 (ppmv)	C1 (ppmv)	CO2 (ppmv)	C2 (ppmv)	H2S (ppmv)	C3 (ppmv)	i-C4 (ppmv)	n-C4 (ppmv)	i-C5 (ppmv)	i-C6 (ppmv)	n-C6 (ppmv)	C1/C2	C1/C2+

164-991A-															
6H-1	47.6	NA	NA	117100	NA	89		3	NA	NA	NA	NA	NA	1316	1273
6H-4	52.1	116000	487000	349700	22900	275	7200	12	4					1272	1202

164-992A-															
6X-3	45.7	37000	158000	747600	32700	1248		13.3	3.9	0.3	0.1	0.2	0.1	599	590

"Notes: Oxygen (O2) and nitrogen (N2) concentrations are included as a guide to the amount of air contamination in each sample. C1 through C6 = the alkanes: methane, ethane, propane, butane, pentane, and hexane. "															
"Iso- and normal configurations of butane, pentane, and hexane are designated with i- and n- prefixes. C1/C2 = the methane/ethane ratio, and C1/C2+ = the ratio of methane/the sum of (C2 through C6). NA = not analyzed."