Combined with quantitative determination of concentration and isotopic composition of petroleum hydrocarbons, weathering simulation experiments on artificially mixed oils and their two end-member oils are performed for identification and quantification of mixed sources. The >C18 n-alkanes show no appreciable losses during a short-term weathering process. An approach based on distribution of longchain n-alkanes (>C18) is suggested for estimating the contribution proportion of each source in mixed oils. Stable carbon isotope profile of individual n-alkanes is a powerful tool to differentiate sources of oil spills, but unavailable to accurately allocate each contribution due to a relatively large analytical error. IsoPrime 穩(wěn)定同位素質(zhì)譜儀