Abstract: Carbazoles are polar compounds in oils,and they are useful indicators for study of hydrocarbon migration.In oil migration,carbazoles have effects with and can be adsorbed to country rocks;Benzoacarbazole migrates faster than benzoccarbazole;C₃-carbazole has smaller polarity than C₂-carbazole and the former can migrates faster.Therefore,with increasing the migrating distance,amount of carbazole in oil decreases,Benzoacarbazole/ benzoccarbazole ratio increases,and C₂-carbazole/C₃-carbazole value reduces.The second period of hydrocarbon reservoir formation in the Tarim Basin took place in later Hercynian.In Hercynian,the Awati Sag kept subsiding,and it was the major hydrocarbon-generating sag in the Tarim Basin.At that time,the Cambrian-lower Ordovician source rocks in the Awati sag were in the phase of large-scale hydrocarbon expulsion,and based on the above-mentioned indices of nitrogen compounds,the expelled hydrocarbons migrated in all directions from the hydrocarbon generation center and were trapped in structural highs.These hydrocarbon pools rose to the surface in the end of Hercynian and the hydrocarbons formed widely distributed dry asphalts.