130 natural gases in the continent of China were determined for the abundance and carbon isotopes of hydrocarbons and carbon dioxide. The δ 13 C (PDB) values of methane range from −68 to − 24.4%, and the largest isotopic variability for hydrocarbons is of δ 13 C 1 < δ 13 C; < δ 13 C; < δ 13 C 4 < δ 13 C 5 . These characteristics suggest that the gaseous hydrocarbons originated principally from thermal and or microbial decomposition of organic matter. The wide variations of δ 13 C 0 distribution patterns (n = 1, 2, 3, 4 and 5) can be explained by (1) extensive mixture between thermogenic and microbial gases, or between thermogenic gases produced during different thermal stage, and or (2) preferential microbial oxidation. There is no direct evidence for the presence of abiogenic hydrocarbon in natural gases in China. One sample from Songliao basin shows a heavier δ 13 C 1 ( − 24‰) and reverse isotopic distribution pattern ( δ 13 C 1 > δ 13 C 2 > δ 13 C 3 ). Concerning the occurrence of mantle-derived He, Ne, Ar and Xe in the south Songliao basin, we propose that the methane mantle derived and heavy hydrocarbons (ethane, propane, butane, etc.) formed from polymerization of the mantle-derived methane. The δ 13 C values for carbon dioxide range from − 13.9 to + 13.5‰ suggesting the multiple origins. Gases with CO 2 concentrations greater than 10% have a narrow range of δ 13 C values, from − 8 to − 2‰, and show higher 1 He 4 He ratios ( > 0.1 times the atmospheric value), suggesting that a mantle-derived component is diluted by CO 2 derived from carbonate and or organic matter. Positive δ 13 C values ( + 4 – + 14‰) indicate CO 2 reduction to CH 2 , CO 2 with trace concentration in CH 4 -rich gases can be attributed to microbial decomposition of organic matter in sedimentary rocks.