An in-house designed and manufactured on-line analyzing device consisting of vacuum ball milling

heating releasing

helium purging and liquid nitrogen trapping was used to study the light hydrocarbon fractions(C

5

-C

13

) of scattered organic matter in source rocks.Ten source rock samples and saturated hydrocarbon samples of their extracts as well as 15 oil samples from the Eocene Shahejie Formation in Dongying and Zhanhua depressions of Shengli oilfield were first analyzed by GC and GC-MS.Then oil-source and oil-oil correlation and classification of light hydrocarbon(nC

6

-nC

9

) were performed.The results in combination with the biomarkers and geological background were finally used to perform comprehensive study

leading to four conclusions.(a)The light hydrocarbons in the scattered organic matter of the source rocks in the upper Es

4

lower Es

3

and Es

1

are different in chemical compositions.(b)The chemical components of C

5

-C

13

light hydrocarbons are related to the salinity of water column during deposition

which is consistent with that of the oils.(c)Among the 15 oil samples

8 samples contain light hydrocarbons mostly originated from the lower Es

3

source rocks

while 4 samples from the upper Es

4

source rocks

the rest are mixed oil.(d)The on-line device provided a new way for study the characteristics of light hydrocarbons(C

5

-C

13

)in the scattered organic matter in source rocks and their application in petroleum geochemistry.