Static pyrolysis of Methanobacterium thermoautotrophicum (M.t.) and Methanosarcina barkeri (Ms.b.) at 330°C for 3 days in the presence of water (but in the absence of minerals) produced pyrolysates from which small amounts (<1% of heated dry cell mass) of aliphatic hydrocarbons were isolated. In M.t. the hydrocarbons comprised a complex mixture of C 15–40 acyclic isoprenoids with head-tail, tail-tail and head-head linkages whilst in Ms.b., a much simpler distribution was observed [confined essentially to the head-tail isoprenoids pristane (C 19) and phytane (C 20) and the tail-tail linked 2, 6, 10, 15, 19-pentamethyleicosane (C 25)]. In both pyrolysates the ratio of Pr/Ph was >1. The distribution of head-head isoprenoids was similar, but not identical, to that found in some crude oils and sedimentary rocks in which the distributions have been said to result from natural maturation of methanogen lipids. Artificial maturation by pyrolysis suggests that such compounds are indeed good biomarkers for methanogens. The low amounts of head-head hydrocarbons in the pyrolysates suggests either that their presence in crude oils is due to quite larger contributions from methanogens or that pyrolysis underestimates the production of hydrocarbons for methanogens. Since pristane and phytane are more abundant in the M.t. pyrolysate than any of the head-head isoprenoids it is possible that the Pr/Ph ratios of crude oils in which head-head isoprenoids have been identified, have also been affected by hydrocarbon generation from methanogen lipids. Furthermore, since the Ms.b. pyrolysate also contained Pr and Ph but no head-head isoprenoids, it is possible that the pristane and phytane distributions of some crudes which do not contain head-head isoprenoids may yet have been affected by methanogen-derived lipids. However, the data set in this report is limited and further experiments would be needed to confirm this.