A study funded by the U.S. Department of Energy, the Gas Research Institute, Mobil Exploration and Producing U.S., and Altura Energy was done to determine geologic controls on deep, prolific Ellenburger gas reservoirs at Lockridge, Waha, West Waha, and Worsham-Bayer fields in Pecos, Reeves, and Ward Counties in West Texas. A major component of the data base amassed for the study was a 176-mi2 3-D seismic survey extending across these fields. Ellenburger (Ordovician) reservoirs occurred at depths of 17,000 to 21,000 ft (5200 to 6400 m) over most of the study area. The eastern half of the 3-D seismic survey was covered with a thick (500 to 2000 ft [150 to 600 m]) variable layer of low-velocity Tertiary fill underlain by a varying thickness of high-velocity salt/ anhydrite. These near-surface conditions attenuated seismic reflection signals from deep targets and made static corrections of the data difficult. The 3-D seismic data acquired in this study are thought to be some of the best quality data produced over these fields, yet the 3-D image of the deep pre-Pennsylvanian targets was of limited quality because of the combined effects of complex, attenuating, near-surface layers and weak reflection signals from deep seismic targets. The principal interpretation objective was to construct the complicated tectonic structure related to these fields to determine genetic relationships between faults and deep gas production. The challenge was to construct this structural picture from a 3-D seismic image that did not provide a clear, unambiguous picture of the fault systems. Petrophysical analyses of logs from wells drilled at key structural locations were invaluable in interpreting fault geometry by identifying overturned beds and repeated sections. Once 3-D seismic horizon and fault interpretations were done across the complete 176-mi2 area, depth maps of key pre-Pennsylvanian horizons were made, and vertical depth sections were constructed across critical structural areas. The seismic interpreted structures were then restored to pre-deformation conditions to verify that the pre- and post-deformation lengths of these key horizons were consistent, and thereby determined if the seismic fault interpretations were structurally valid. These methods of integrating petrophysical analyses and section reconstructions into the interpretation of 3-D seismic data should be helpful to others who are confronted with the challenge of constructing complex structural models from limited-quality 3-D seismic images.