The lower Wilcox sand deposits encased between two continuous erosional sequences are of good reservoir quality and usually gas productive. However, the distribution of sedimentation is laterally scattered and hard to interpret in seismic data. Simultaneous inversion of petrophysical parameters such as P-impedance, S-impedance, and density by the integration of pre-stack data and well logs allows us to quantitatively characterize the reservoirs, and to distinguish them from the surrounding rocks. In this study, we use pre-stack inversion of the petrophysical parameters for the gas reservoir in an analog field. For wells that are missing sonic and density logs, we estimate the parameters using the time average equation and Gardner's equation, respectively. The estimation results are verified using well log correlations. Rock physics analyses are conducted to find the optimal parameters to characterize the producing sand. Our inversion results show a successful delineation of the reservoir using the Vp/Vs value. In addition, the sandstone is mapped in the crossplot of the inverted results.