The 198 metre core of Quaternary sediments obtained from Hole 147, Leg 15 of the Deep Sea Drilling Project was laid down under anoxic conditions in the Cariaco Trench below 882 metres of water off the coast of Venezuela. Pockets of gas from core depths between 45 and 180 metres were found to be 86-99% methane. The carbon dioxide content of the ten pockets sampled reached a maximum at about 130 metres. Isotopic analysis of the methane showed delta (super 13) C PDB values between -59 and -76%o. This is consistent with a biological origin due to the anaerobic reduction of organic matter in the sediments. The D/H ratios of the methane in all samples were similar, with a mean delta D SMOW value of -178%o. In carbon dioxide delta (super 13) C PDB and delta (super 18) O PDB both fell in the range of +0.5%o to -4.5%o and both values approached zero on the PDB scale as depth increased.