A large cooperative field study began in January 1996 and is focused on Lower Paleozoic gas reservoirs in the Permian Basin, West Texas (Figure 1). The purpose is to evaluate development options for prolific, mature, carbonate gas reservoirs in a structurally-complex geologic province. New economic gas reserves likely exist in untapped fault blocks or poorly drained reservoir compartments within the Delaware and Val Verde Basins. Geologic structure and reservoir development is being evaluated utilizing 3-D seismic techniques and a multidisciplinary team approach. The cooperative research is supported by U.S. Department of Energy, GRI, Texas Bureau of Economic Geology, Shell Western E&P Inc., Mobil E&P U.S. Inc., Landmark Graphics, Schlumberger, Petroleum Information Inc., and Tobin Data Graphics. Part 2 Electrical images in boreholes are becoming increasingly important in interpreting the rock record. In addition to identifying fractures and faults, borehole imaging tools are used for a variety of other applications such as horizontal drilling, environmental studies, stress orientation measurement studies, sequence stratigraphy, paleotransport, facies, and diagenetic analyses. These tools produce electrical microconductivity images of the wellbore, which are interpreted using an interactive graphics workstation. High-resolution (~ 2.5-mm) and nearly complete borehole coverage can greatly increase the detail and precision of geological interpretations. Yet, to be fully useful, borehole images should be calibrated with core. This study provides the first comprehensive comparison of carbonate features in cores with a suite of all currently available electrical imaging logs. The Lower Ordovician Ellenburger Group, West Texas, serves as a model for a dolomitized, fractured, karsted, and brecciated carbonate reservoir. Characteristic reservoir features, including fracture breccia, chaotic breccia, laminated mudstones, grainstones, and bioturbation are identified both on electrical imaging logs and in cores. Electrical images provide more complete information than cores in cavernous and highly fractured zones because cores commonly show no recovery or occur as rubble in these zones, which are the most productive zones in the Ellenburger reservoir. Borehole imaging, therefore, provides in-situ visualization of cavernous porosity, chaotic breccias or conglomerates, and highly fractured intervals, as well as other key insights into karst stratigraphy.