Two active hydrothermal vent sites on the East Pacific Rise (EPR) at 13°N and 21°N have similar biogeochemicals. They are characterized by large animal communities surrounding massive porous mixed mineral (e.g. sulfide) edifices venting hot water (200–350°C) as black smokers. An analogous vent system on the Mid-Atlantic Ridge (MAR) at 26°N has also been studied. Sediment (talus), mound mineral and water samples from these areas were analyzed in terms of biological marker lipids such as normal and isoprenoid alkanes, polynuclear aromatic hydrocarbons, triterpanes, steranes and fatty acids to describe their sources, bacterially-mediated transformation products and alteration by hydrothermal fluids. The mixed interior/exterior of a chimney at 21°N on the EPR shows a series of iso- and Anteiso-alkanes which are known constituents of high wax crude oils. These alkanes, coupled with the absence of triterpanes and steranes seem to indicate a higher temperature, water-soluble fraction from hydrothermal pyrolysis which is unfavorable for the preservation of the biomarkers. Chimney fragments with tube worm casts at 21°N contain products that are characteristic of immature biodegraded organic matter as indicated by microbial markers (branched C 15 and C 17 fatty acids) and low thermal alteration which enhanced formation of cholestene isomers and diacholestenes. In comparisons, a metalliferous sediment and sediment trap particles at 13°N on the EPR contain a biomaker mixture, namely recent biomarkers derived from early diagenetic transformations of biogenic compounds (sterols, squalene) and more mature components [5α(H), 14β(H), 17β(H) steranes (20 R + 20 S), dominant 17α(H)-hopane series], both having the same origin. Hydrocarbons isolated from hydrothermal anhydrite, chalcopyrite and sphalerite-enriched samples from 26°N on the MAR exhibit a high degree of thermal maturation, compared to an Fe-oxide-enriched sample, as evidenced by the high abundance of low molecular weight n-alkanes ranging from C 14 to C 25 with a broad distribution of naphthenes. All these trace hydrothermally derived petroleums contain polycyclic aromatic hydrocarbons (PAH). The Fe-oxide-enriched sample has a lower content of PAH than the other mineral samples; however, benzopyrenes and coronene are present at significant levels and a series of mature triterpanes is also detectable. These trace levels of petroleum with the associated biomarkers and PAH strongly suggest generation from contemporary organic detritus by hydrothermal activity and subsequent association with the minerals, talus, vent fluids, and ambient water.