Molecular geochemical methods have shown that it is often diﾁcult to diﾀerentiate between coal-and interbedded shale-sourced oils, even though coals and interbedded shales may exhibit considerable organic inux variation (e.g. land plant vs algal organic matter) due to the changes of depositional setting. However, compound-specirc stable carbon isotopic compositions are sensitive to the source input variations. Typically, specirc molecules are more depleted in 13C with increasing content of aqueous biota. This hypothesis is examined and exemplired by comparing the stable carbon isotopic ratios of n-alkanes from source rock extracts and related oils of the Turpan basin, north-western China. Stable carbon isotopic values of n-alkanes extracted from coals and interbedded shales show that d13C values of n-alkanes with less than 20 carbon atoms vary only slightly. However, there are dramatic changes in the isotopic compositions of higher molecular weight n-alkanes. Furthermore, n-alkanes from coal extracts are enriched in 13C relative to that of interbedded shales with excursions up to 2-3%. This comparison enables the dio erentiation of coal-and interbedded shale-sourced oils, and provides information useful in assessing the hydrocarbon system of a basin.