Pore free hydrocarbons and inclusion hydrocarbons in 6 Silurian bituminous sandstone samples from the Tazhong area of Tarim basin are separated and analyzed with GC and GC-MS.The analysis results show that pore free hydrocarbons and inclusion hydrocarbons have different characteristics.The pore free hydrocarbons are represented by light hydrocarbons of pre-peak distribution and peak carbon number at nC

16

or nC

20

without odd carbon number predominance

which are usually associatee with significant biodegradation.The inclusion hydrocarbons are represented by heavy hydrocarbons of bimodal distribution and peak carbon number at nC

25

or nC

29

with odd carbon number predominance.In respect of biomarker

the pore free hydrocarbons have a relatively high concentration of tricyclic terpanes and pregnane

with the C

27

C

28

and C

29

steranes of asymmetrical "V" distribution;whereas the inclusion hydrocarbons have a relatively low concentrations of tricyclic terpanes and pregnane

with the C

27

C

28

and C

29

steranes of oblique-ascending distribution.Oil-source correlation indicates that the hydrocarbons entrapped in the inclusions of bituminous sandstone might be sourced from the Middle-Lower Cambrian source rocks

while the pore free hydrocarbons might be generated by the Middle-Upper Ordovician source rocks.