Pennsylvanian petroleum pools in southern Paradox basin are in algal carbonate mounds of Desmoinesian age elongated in a general northwest direction along the basin shelf. Carbonate reservoirs are associated closely with sapropelic black shale and evaporite, which occur in cyclic repetition in the shelf area and grade basinward to a predominantly salt section. All reservoirs appear to be isolated bodies of porous carbonate, mostly limestone. About 30 fields productive from the Pennsylvanian have been found; aboout half are classed as stratigraphic and the other half as either structural or structural-stratigraphic. In almost all fields it can be demonstrated that accumulation would have formed even if no structural closure were present. Aneth, Ismay, and Cache fields are good examples showing major stratigraphic and only minor structural influence on accumulation.