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Carbon isotopic compositions are effective indicators for gas origin identification.

Coal-type gas possesses heavier carbon isotopes of ethane and propane compared with oil-type gas.

A positive relationship of δ¹³C₂ and δ¹³C₁ and δ¹³C₃ suggests that the thermal genetic gases from organic matter cracking under high temperature and pressure are a dominant source in the Tarim basin.

GOR-isotope quantitative model can apply to the understanding of natural gas-formation and gas-filling history.