d13C of Alkylnaphthalene is mostly controlled by maturity Stable carbon isotopic compositions of individual aromatic hydrocarbons in petroleum: Origin and formation of low-molecular-weight aromatic hydrocarbons (LMWAHs) Pierre Le Métayer, Kliti Grice, Ercin Maslen, Luc Fusetti, WAOIGC, Department of Applied Chemistry, Curtin University of Technology, Perth, Australia d13C of individual LMWAHs in crude oils and sediments of varying age, facies type and thermal maturity have been investigated in order to understand the influence of both thermal maturity and source on the d13C of LMWAHs. Positive trend in d13C of ANs as the degree of methylation decreases for few samples but no significant correlation between d13C of APs and degree of methylation for most of our oils d13C of APs isomers characterized by a high standard deviation, which would be indicative of varying origin. d13C of alkylphenanthene is mostly controlled by sources Positive trend in d13C of ANs as the degree of methylation decreases Barrow Island and Pasco oils vs. more mature oils (a) or more immature oils (b): maturity directly affects d13C of ANs. 13C fractionation related to an isotopically depleted ‘methyl pool’ with increasing maturity. d13C of DMNs, TMNs and TeMN natural isomers from Moorari show large variation (cf. b) testifying that, for few specific oils, source is also a factor impacting on d13C of ANs. d13C of Alkylnaphthalene is mostly controlled by maturity