Abstract: There is considerable debate concerning the ages of a 5.6m-thick dolostone sequence in the Yanwang valley of Xikou, Yuechi, Sichuan which was interpreted as the “Carboniferous” gas beds by the previous workers. It is contended in this paper that the dolostone sequence were developed as reef complexes in the late Early Silurian, therefore they should be of Silurian age rather than of Devonian or Carboniferous ages.. The seaward side of the shallow marine shelf uplifted in the later stage of the Caledonian orogeny should be considered as a new field of hydrocarbon exploration. The higher indices for oil generation have been identified for the Longmaxi Formation in the lower part of the Lower Silurian strata, and the reef complexes with good reservoir behaviors have also been recognized in the upper part of the overlying Lower Silurian strata overlapped by the Carboniferous strata east, of the Huaying Mountains and interpreted as the highly productive gas beds in the study area.