Porosity development and reservoir distribution in the Permian rocks of the Bighorn basin were strongly controlled by the first- and second-order paleotectonic elements active in the Wyoming shelf. First-order elements, including the Greybull arch, Bighorn high, and an extension of the Yellowstone high, defined the basin geometry and regional paleogeography, influenced the distribution of clastic vs. carbonate lithofacies, and controlled the areal extent and degree of porosity enhancing dolomitization. Second-order tectonic features, related to drape and/or movement along syndepositional basement fault systems, also influenced patterns of Permian sedimentation by providing localized sites of differential subsidence and subtle but persistent paleobathymetric relief. Among the most significant exploration targets in the basin are the trends of peritidal and restricted marine reservoirs in the Franson and Ervay Members. Porous dolomites in these facies developed within and adjacent to two separate shoaling trends. Contrary to popular belief, these trends do not represent true carbonate shorelines. Rather, they define a fairway of discontinuous island-peninsula complexes bounded on the west by more open-marine carbonates and on the east by a broad, restricted lagoon or salina filled with subaqueous evaporites and siliciclastics. The trends of the peritidal facies are centered over underlying tectonic elements. The relatively unexploredmore » fairway in the Franson Member is centered over a northwest-trending extension of the Yellowstone high. Equivalent facies in the Ervay are offset to the east, paralleling the faulted western margin of the ancestral Bighorn high.« less