Two basic types of lower Morrowan Sandstones were deposited in a broadly transgressive system in the Anadarko basin. Their reservoir capacity has been profoundly altered by diagenesis. Type A is a nearshore, clean, well sorted, nonglauconitic, noncalcareous sandstone deposited in a high energy environment. It now shows either extreme pressure solution or secondary quartz overgrowth and is permeable only where it is medium- to coarse-grained. Type B is a seaward facies of Type A, deposited under lower energy conditions and is normally poorly sorted, "glauconitic," calcareous, and, in part, shaly. It now shows minor secondary quartz overgrowth and pressure solution, extensive carbonate cementation, and some authigenic clay. It is permeable in random-shaped areas that have undergone secondary removal of carbonate cement.