Test results of different types of crude oils show that pyrrolic compounds such as carbazole

benzocarbazole and dibenzocarbazole are found

and the first two types are predominent.The relative abundance of the homologues of these two types show normal distribution

which is closeby related to source material types and the effect of oil and gas migration and thermal maturation.The crude oil that was mainly derived from high plant contains relatively more alkylbenzocarbazole and dibenzocarbazole;the increase of oil and gas migration distance could result in the enrichment of carbazole series;the increase of maturity could increase the enrichment of low molecular weight compounds.The pyrrolic compounds have various isomers

this might be related to different mother materials of kerogen.