Analysis of the geochemical characteristics of natural gas from the main structural units of the Kuqa Depression in Tarim Basin shows that the natural gas from Dabei-Kelasu structural belt is dominated by methane and has a dryness coefficient [C

1

/(C

1

-C

5

)] near 1.00

indicating typical dry gas;while that from the frontal uplift zone has a relatively low content of methane and a dryness coefficient less than 0.95

indicating typical wet gas.In terms of carbon isotope compositions

the gas from the Dabei-Kelasu structural belt contains significantly heavier methane and ethane isotopes(

>

-31‰ and-20‰

respectively)

while that from the frontal uplift zone has obviously lighter methane and ethane isotopes(

<

-33‰ and-20‰

respectively).Maturity calculation reveals that the gas from the Dabei-Kelasu structural belt belongs to over-mature gases with a vitrinite reflectance ranging between 1.65% and 2.25%

while that from the frontal uplift zone belongs to highly-mature gas with a vitrinite reflectance ranging from 1.00% to 1.35%.All these indicate that the natural gases in different structu-ral units in the Kuqa Depression were generated from the organic matters in the source rocks at different thermal evolution stages.