Immature oils

especially immature commercial oils

are of key importance both in theory and practice.Guanghua anticline of Jianghan salt-lake basin of Paleogene is one of the oil-bearing structures which have certain amount of petroleum.According to data of structural feature and lithological complex

Guang-33 oil produced at the depth of 1829.3-1929.6m of the anticline is thought to be indigenous

of which the vitrinite reflectivity is 0.45-0.5%.Quantitative study of biomarkers shows that the oil has a high content of phytane

steranes and triterpanes as well as nickel porphyrin which are of special significance.Compared this very high content of biomarkers with that of immature salt-lake source rocks

it can be seen clearly that the maturity ofthe oil is quite low indeed

and the molecular variations have not yet been polluted too much.Thus an inference can be drawn from molecular variations

especially from DPEP/(DPEP+ETIO)ratio

that the maturity of the oil isestimated to be equal to R?0.43%.Based on the data of structural feature

maturity of reservoir rocks and biomarker quantitative and qualitative study

it can be concluded that theGuang-33 oil is a typical immature commercial oil formed in salt-lake environ-ment.