Problems of accumulation of oil and gas in the Newcastle sandstone (Upper Cretaceous) involve facies changes from shale to sandstone which are recognized most clearly in the Mush Creek and Skull Creek area. Well-sample and electric-log information from 200 wells in the area has afforded details to classify five sand beds which underlie the datum bed at the top of the Newcastle sandstone. The structure on outcrops and on the subsurface datum bed is a monoclinal, southwest dip of approximately 2°, formed in late-Cretaceous time (Laramide orogeny). The type log describes the lithologic character of the five sand beds and shale inter-beds. Cross sections and lithofacies maps of the respective sand beds illustrate the facies changes in the Newcastle sandstone. The accumul tion of oil in the area is directly related to the porosity, permeability, and thickness of each sand bed. The post-Cretaceous monoclinal southwest dip on the Newcastle sandstone does not form a structural trap, and does not appear to have caused any appreciable migration of the oil in the respective sand beds. The oil accumulation apparently is closely related to the local stratigraphic and geographic site of the origin of the oil. Recognition of lithofacies changes in the Newcastle sandstone now has been widely accepted and is being utilized in a broad exploratory program.