In the axial zone of the Abakaliki Basin (southern Benue Trough, Nigeria), Middle Cretaceous shales have undergone normal regional burial which is superposed by Santonian tectonism and local heating effects around hydrothermal centres (Ishiagu, Enyigba, Ameri). Illite crystallinity, IC ranges from 0.4 to 0.9 °2Θ, smectite proportion in mixed-layer illite/smectites, S = 0 % and reflectance of vitrinite, Rm ranges over broad limits of 2.46 to 4.30 %, all indicating strong diagenetic to anchimetamorphic transformations. The Upper Cretaceous shales outside the axial zone and in the Anambra Basin have only been exposed to normal burial diagenesis in areas around Ezillo, Ihe and Leru-Okigwe. In these locations, IC = 1.4 to 1.6 °2Θ, S varies from 20–30 % and Rm between 0.7 and 0.9 %. Paleotemperature estimates are up to 230 °C in the axial zone and about 100 to 140 °C in the marginal areas. The fairly mature Late Campanian Enugu/Nkporo Shales are possible source beds for liquid petroleum whereas the Turonian Eze-Aku Shales are more gas prone. The Albian Asu River Shales are overmature and contain gas prone organic constituents.