We compare the Second White Specks and Belle Fourche Formations (2WS/BF) of Alberta, Canada to the Eagle Ford Formation shale (EF) of southern Texas and, to a lesser extent, the Tuscaloosa marine shale (TMS) of Louisiana and Mississippi. These units were deposited during the same Late Cretaceous (Cenomanian–Turonian) eustatic rise and highstand, and all are prolific source rocks. Our aim was to define the reasons why attempts to develop the 2WS/BF as a resource play were unsuccessful. We propose that failure was controlled by the combined effects of three geologic factors—reservoir quality, organic richness, and completion quality—all of which stem from the depositional setting and history of the interval. Because it was deposited in close proximity to a major source of fine-grained siliciclastic sediments, the 2WS/BF has a higher clay-mineral content than the EF, the latter being deposited in a relatively clastics-starved setting. Porosity loss, through compaction, was therefore greater in the 2WS/BF, and the higher clay-mineral content of that play, combined with the stratigraphic stacking, led to completion problems such as proppant embedment and out-of-zone growth of hydraulic fractures. The TMS was likewise challenged as a resource play because of its high clay content. The original organic content of the 2WS/BF was neither as high nor as oil prone as that of the EF because of paleoenvironmental conditions at the seafloor at the time of deposition. This retrospective analysis identifies depositional setting as a first-order control on the potential of a source rock to form a resource play.