The vertical fades sequence comprising the Upper Devonian Duperow and Birdbear (Nisku) formations in the Williston Basin reveals three major shoaling-upward depositional cycles, punctuated by more frequent salinity cycles expressed as remarkably widespread anhydrite and argillaceous marker beds. Identification of syndepositional structures, many coincident with structures, was gained through isopach mapping of intervals bounded by these marker beds. Excellent examples of reservoir development under paleostructural control are illustrated for Duperow Unit 4 in the Billing Nose area by the Tenneco Gawryluk #1-30 and Federal #2-30 cores and for the Birdbear (Nisku) in the Wolf Creek Nose area by the Murphy Sethre #1-B and Sletvold #1-B cores. In both examples, the paleostuctures represented relative paleotopographic highs and, as such, influenced the local development of favorable reservoir fades. Duperow Unit 4 skeletal banks, dominated by globular stromatoporoid floatstone, formed over the crest of the Billings Nose paleostructure. Birdbear (Nisku) skeletal banks, comprised of Amphipora wackestone, and packstone and platy stromatoporoid boundstone, formed along the flanks of the Wolf Creek Nose paleostructure, while the crest of the structure sustained peritidal deposition unsuited for bank development. Dolomitization of skeletal bank facies and portions of adjacent fades was the mechanism for reservoir development. Mg⁺⁺ -enriched brines expelled from overlying evaporites during burial compaction provided the dolomitizing fluids in both examples, although the style and magnitude of dolomitization was regulated by the facies distribution and early burial history peculiar to each. Migration of dolomitizing fluids and hydrocarbons was facilitated by fracturing of intervening lithified strata. Sources for both fluids are believed to have been within readily defined stratigraphic intervals.