Abstract: The lithic arkose and feldspathic litharenite as the main sandstone types in the fourth member of the Quantou Formation in western Longhupao region,Songliao Basin are characterized by low compositional maturity,fine grain sizes and moderate to poor sorting.The statistical data have revealed that the physical properties of the hydrocarbon reservoirs are getting better with the increase of quartz contents,and worse with the increase of lithclastic contents,indicating that the compositional maturity may have exerted an important effect on the pressure resistance,response of compression and physical properties of the hydrocarbon reservoirs.Other influencing factors for the physical properties of the hydrocarbon reservoirs include fine grain sizes,poor sorting and higher contents of interstitial materials in the sandstones from the fourth member of the Quantou Formation.