Crude oils of different ages (J

2

E

3

-N

2

1

and N

2

2

)from Qaidam basin can be divided into three types according to the patterns of distribution of hydrocarbons on chromatogram.Among them.the maturity of crude oil J

2

is higher.The main peak carbon of normal pararffins is C

15

and the pristane to phytane ratio is 2.44—2.90.Crude oils E

3

-N

2

1

are characterized by higher Phytane peak than other.The pristane/phytane ratio 0.86—0.52

and the main peak carbonof normal paraffins commonly is C

22

.It is obvious that even carbons play a dominant role on chromatogram of normal paraffins.For crude oil N

2

2

the light components take a prevailing place.The main peak carbon of normal paraffins is C

13

while the pristane/phytane ratio is 1.26.In N

1

and N

2

1

there are some crude oils formed by degradation

in which the action of microbes is of prime importance.Neady all normal paraffins are degraded by microbes

therefore

th

e isoprenoids are the foremost on the whole hydrocarbon chromatogram.Questions of migration of crude oils are also tentatively discussed here.