The Karoo Basin of South Africa was explored for conventional oil and gas in the 1960s, and during which 19 boreholes were drilled by SOEKOR-the Southern Oil Exploration Corporation. Ten of these boreholes in the southern part of the basin were deep, c. 2.3 to 5.5 km in depth. Geochemical, petrophysical and petrographic studies on the recovered cores from these drill holes concluded that the lower Karoo sequences were possibly prospective for thermogenic gas across the Karoo region immediately north of the Cape Mountains and south of the main concentration of dolerite intrusions flanking the Karoo Escarpment. Since then, very limited analytical work has been undertaken on these cores to gain new data and to extend the concepts towards potential shale gas plays. In the light of the recent interest in unconventional shale gas potential of the Karoo Basin, we re-examine this SOEKOR data and, together with new petrographic and geochemical analyses on 115 core samples from eight of the deep drill holes, we present new resource estimates of two possible reservoirs with recoverable shale gas of 10 to 50 Tcf (Source Rock 1) and 65 to 400 Tcf (Source Rock 2), respectively.