The Upper Triassic source rocks in the central of western Sichuan Depression got mature during the deposition of the 3

rd

member of Xujiahe Formation

over-mature stag in the late of Early Jurassic and post-mature in the Late Jurassic.The EW-dipping tectonic framework in western Sichuan depression determines that the source rocks in the west got mature earlier and have higher maturity than that in the east.Area with high maturity was near the piedmont of Longmen Mountain at the end of deposition of the 3

rd

member of Xujiahe Formation

and it extended eastwards with the highest maturity migrating near to Longshen-1 well at the end of deposition of the 5

th

member of Xujiahe Formation.Later it migrated eastwards as a whole at the end of the Jurassic.The area with high maturity has centered in Mianyang-Deyang-Pengzhou-Dayu from the Creataceous to present

with the highest maturity occurring at Mashen-1 well and Dayu North.The whole amount of gas generated from source rocks in the Xujiahe Formation in western Sichuan depression is 167.812 5 tcm.The gas generated during the deposition of the Maantang Formation-3

rd

member of Xujiahe Formation accounts for 2.53% of the total

that during the deposition of 4

th

and 5

th

members of Xujiahe Formation accounts for 10.84%

that in the Early and Middle Jurassic 22.97%

that in the Later Jurassic 22.86% and that in the Early Cretaceous 40.97%.