With the newly obtained carbon isotope data for the natural gas, a pilot study of multiple-sourced alkanes related to the mantled-derived fluid is presented. The carbon isotope values of alkanes in the Dongying Sag possess the features indicating a general organic origin. However, there are two sub-populations in the isotopic data set, which reflect two specific types of origins. In general, the sub-population with high δ13CCH4 values is related to the CO2-rich, mantle-derived fluid, and it is distributed in the belts where mantle-derived fluid flow and basic volcanic activities have occurred. Geological and geochemical studies demonstrate that this variation of methane carbon isotope values in the Dongying Sag is unrelated with the basin bury and thermal histories, types of source rocks, and reactions between basin fluid and rocks. Mixing of mantle-derived fluid and organic sourced hydrocarbons is probably the cause for the variation. The carbon isotope values ​​of alkanes in the Dongying Sag possess the features features a general organic origin. However, in the newly acquired carbon isotope data for the natural gas, a pilot study of multiple-sourced alkanes related to the mantled-derived fluid is presented. , there are two sub-populations in the isotopic data set, which reflect two specific types of origins. In general, the sub-population with high δ13CCH4 values ​​is related to the CO2-rich, mantle-derived fluid, and it is distributed in the belts where mantle-derived fluid flow and basic volcanic activities have occurred. Geological and geochemical studies demonstrate that this variation of methane carbon isotope values ​​in the Dongying Sag is unrelated with the basin bury and thermal histories, types of source rocks, and reactions between basin fluid and rocks. Mixing of mantle-derived fluid and organic sourced hydrocarbons is probably the cause for the variation.