Phenylalkanes with carbon numbers between 16 and 19,characterized by the main carbon-18,have been identified in the mod-em sediments collected from gas hydrate area from the Gulf of Mexico.The structure of phenylalkanes with four isomers for ever-y carbon number was determined by means of their mass spectra and previous studies.The distribution of the series character-ized by a low molecular mass was similar to the distribution of n-alkane,alkylcyclohexanes and alkylbenzenes in each sample.There were differences in the distribution of the phenylalkane series between the S - 1,S - 4,S - 7,S - 9 samples and the S -8,S - 10 and S - 11 samples.The phenylalkanes might be derived from Archaea associated with anaerobic oxidation of methane (AOM) processes in S - 1,S - 4,S - 7 and S - 9 samples according to their distribution resembled with the distribution of the extract from a type of Archaea.The distribution of alkylcyclobexanes and alkylbenzenes in S - 1,S - 4,S - 7 and S - 9 sample was found to be similar to each other.The odd-over-even predominance of alkylcyclohexanes was seen as the input of some bac-terial.