In the Healdton field oil is produced mostly from the Pennsylvanian Hoxbar Group and the Early Ordovician Arbuckle Group. The Arbuckle is predominantly carbonate, about 5,000 feet thick, and produces primarily from three dolomite zones in the upper 1,600 feet. The lowest of the three productive units, the Brown zone, is the field's main objective and consists of very permeable dolomite about 600 feet thick. The structural closure exceeds 1,500 feet and the oil column is as much as 700 feet thick. The anticline that trapped the hydrocarbons resulted from the Wichita Mountains-Criner Hills orogenic movement which began in Early Pennsylvanian time and was reactivated in Late Pennsylvanian time. The slightly folded Hoxbar strata lie upon an eroded pre-Pennsylvanian surface; the underlying Arbuckle is faulted and more tightly folded.