Relatively high abundance of C_(31) steranes has been identified from cretaceous source rocks and crude oils in the Songliao Basin, China. C_(31) steranes which occur as ten isomers were tentatively identified as 4, 22, 23, 24-tetrametyhlcholestane based on their retention time and mass spectrum.They bear a lower thermal stability and occur as important components in the immature oils of Chaochang region because they have three-methyl groups in their side chain. The relatively high abundance of C_(31) steranes in the samples can indicate the source input of some special algae in the brackish and saline environment. Therefore they can be used as very useful biomarkers for organic facies analysis and oil correlation. Their biological source perhaps related to the dinoflagellate such as G. foliaceum and P. foliaceum. The gorgostanol are considered as possible precursors for the putative C_(31)4methyl sterane which formed in the stage of diagenesis. Relatively high abundance of C_ (31) steranes has been identified from cretaceous source rocks and crude oils in the Songliao Basin, China. C_ (31) steranes which occur as ten isomers were tentatively identified as 4, 22, 23, 24- tetrametyhlcholestane based on their retention time and mass spectrum. the y bear a lower thermal stability and occur as important components in the immature oils of Chaochang region because they have three-methyl groups in their side chain. The relatively high abundance of C_ (31) steranes in the samples can indicate the source input of some special algae in the brackish and saline environment. They can be used as very useful biomarkers for organic facies analysis and oil correlation. Their biological sources may related to the dinoflagellate such as G. foliaceum and P. foliaceum. The gorgostanol are considered as possible precursors for the putative C_ (31) 4methyl sterane which formed in the stage of diagenesis.