The Tuns and Opuks shales are essentially kaolinitic with subordinate amounts of quartz, illite, and mixed layer clays. The total clay content of the shales varies from 55 to 92% with an average of 76%. The degree of reactivity in terms of their CEC is low and about 12 m.eq/100 mg on the average. The number of samples was, however, too small to be more useful. The high temperature/pressure assessment of the mud systems has revealed that the barite weighted SynTeq mud is more stable thermally and of better viscosity, gel strength, and load-bearing capacity than the other mud systems investigated. The secondarily viscosified Petrofree has some potential but is of low thermal resistance. It is concluded that the SynTeq mud system is generally a better drilling fluid forrocks in the Niger Delta than either Petrofree or KCL Polymer. The SynTeq is, therefore, recommended for adoption in the oil production company drilling operations. It has been re-emphasized as part of our recommendations that new guidelines for the close monitoring of drilling fluids supplied by mud companies and those actually used in the field (during drilling) be put in place.