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We propose the following identification indicators for CO2 of different origins based on data obtained from analyzing the molecular composition of 1198 gas samples, the CO2 carbon isotope values of 390 samples, and the helium isotope composition of 256 samples collected from wells of 16 oil- and gas-bearing basins and gas seepages in China, and reviewing literature on organic and inorganic CO2 throughout the world. CO2 is of organic origin if CO2 content 13CCO22 is of inorganic origin if ^dgr13CCO2 > -8^pmil or CO2 > 60%; and CO2 is of either organic or inorganic origin or a mixtur of organic and inorganic origins if -10^pmil 13CCO213CCO2 values of organic CO2 mainly range from -10 to -22^pmil. In tectonically stable oil- and gas-bearing basins where deep faults and magmatism are undeveloped, organic CO2 occurs almost exclusively. In tectonically active oil- and gas-bearing basins where active faults and magmatism are present or in areas of modern volcanic activity, the ^dgr13CCO2 values of inorganic CO2 range from -2 to -8^pmil and are distributed along faults. The inorganic CO2 with a ^dgr13CCO2 value of 0 ±3^pmil is of metamorphic origin, and that with ^dgr13CCO2 values of -6 ±2^pmil is mantle derived and of magmatic origin. In China, the ^dgr13CCO2 values of inorganic CO2 gas pools range from -3.41 to -8.44^pmil and the helium ratio (R:Ra) is >1, which indicates that these gases are typically derived from the mantle.