Abstract: The secondary pools in the Penglaizhen Formation in the Xinchang gas field,western Sichuan are believed to be lithologic gas pools.The sandstones are considered as the main reservoir beds in the sandstones and mudstones of the Penglaizhen Formation.The de-tailed studies of sedimenary facies of the gas pools,and seismic response of reservoir beds and gas beds indicate that sedimentary microfacies are the main controlling factors on reservoir quality.The favourable reservoir sandstones in these gas pools may broadly be assigned to the deltaic front channel-mouth bar,deltaic plain distributary channel bar and fluvial channel bar microfacies.The distribution of the favourable reservoir sandstone bod-ies tends to concur with that of the three sedimentary microfacies cited above.