The aromatic hydrocarbons from a significant number of oils and source rocks of different source materials and depositional environments have been analysed by GC and GC-MS. Variations in the distributions of the naphthalenes, phenanthrenes, fluorenes, dibenzofurans, dibenzothiophenes, naphthobenzothiophenes and triaromatic steroid hydrocarbons can be used to differentiate samples on the basis of whether they are derived from marine or terrestrial source materials. Furthermore the nature of the depositional environments in terms of salinity or carbonate vs shale can be distinguished on the basis of variations in the distributions of these compounds and the relative proportions of individual components within the total aromatic hydrocarbon fraction.