Experiments on hydrothermal degradation of Pyrococcus abyssi biomass were conducted at elevated pressure (40 MPa) over a 200-450 degrees C temperature range in sapphire reaction cells. Few organic compounds could be detected in the 200 degrees C experiment. This lack was attributed to an incomplete degradation of P. abyssi cells. On the contrary, a wide range of soluble organic molecules were generated at temperatures >= 350 degrees C including toluene, styrene, C-8-C-16 alkyl-benzenes, naphthalene, C-11-C-16 alkyl-naphthalenes, even carbon number C-12-C-18 polycyclic aromatic hydrocarbons, C-15-C-18 alkyl-phenanthrenes and C-8:0-C-16:0 n-carboxylic acids. The effect of time on the final organic composition of the degraded P. abyssi solutions at 350 degrees C was also investigated. For that purpose the biomass was exposed for 10, 20, 60, 90, 270 and 720 min at 350 degrees C. We observed a similar effect of temperature and time on the chemical diversity obtained. In addition, temperature and time increased the degree of alkylation of alkyl-benzenes. This study offers additional evidence that a portion of the aliphatic hydrocarbons present in the fluids from the Rainbow ultramafic-hosted hydrothermal field may be abiogenic whereas a portion of the aromatic hydrocarbons and n-carboxylic acids may have a biogenic origin. We suggest that aromatic hydrocarbons and linear fatty acids at the Rainbow site may be derived directly from thermogenic alteration of material from the sub-seafloor biosphere. Yet we infer that the formation and dissolution of carboxylic acids in hydrothermal fluids may be controlled by other processes than in our experiments.