The test results of nitrogen isotopic samples of several crude oils and kerogens in China's different depositional environments suggest that nitrogen isotope is related to depositional environment. The

15

N of oils formed in fresh water environment is about 0.3%～0.6%;the

15

N ratios of deposits in salt and brackish waters are the heaviest

15

N is generally above 1%;whereas that in Paleozoic marine carbonate rock and the oil from it is below 0 or less than 0.