A series of Palaeozoic marine oils ranging from condensates to very heavy oils from the cratonic region of the TarimBasin, NW China have been examined to delineate oil families. Crude oils from the Mesozoic foreland Kuqa Depressionwere also analyzed for comparison. The genetic family was assessed using bulk hydrocarbon isotopic composition,alkylation pattern of polycyclic aromatic hydrocarbons (PAHs) and biomarker distributions. Detailed oil–oil correlationsuggests two distinct families occur in the cratonic region. Despite the diversity of the reservoir rocks and somevariability in oil physical properties, the Tabei and Tazhong oils are classified, in general, into a single family, witha possible indication for secondary subdivision. These oils are characterized by low pristane/phytane (Pr/Ph) ratio, highdibenzothiophene/phenanthrene (DBT/P) ratio, light bulk isotopic composition, high degree of PAH alkylation, highproportion of C23 and C24 tricyclic terpanes and low abundance of C24 tetracyclic terpane and triaromatic dinosteroids.This family is inferred to have a Middle–Upper Ordovician source rock. The Tadong family, distinctly different fromthe Tabei and Tazhong families, is characterized by relatively high Pr/Ph ratio, low DBT/P ratio, slightly heavier bulkisotopic compositions and low degree of PAH alkylation. It also has a unique biomarker signature, with a high proportionof triaromatic dinosteroids, possibly indicating Cambrian–Lower Ordovician source rocks.The oils from the Kuqa Depression are easily distinguished from the other two families due to their terrigenous origin.The major characteristics of the Kuqa oils are high Pr/Ph ratio, very low DBT/P ratio, heavy bulk isotopic composition,low PAH alkylation degree, high proportion of C20 and C21 tricyclic terpanes and C24 tetracylic terpane, andabundance of triaromatic dinosteranes and 4-methyl-24-ethyltriaromatic cholestanes. These characteristics are consistentwith terrestrial organic source rocks deposited under sub-oxic conditions.