Abstract: An organophilic clay mixture having a first organophilic clay that is modified attapulgite clay and/or modified sepiolite clay, together with an organophilic modified bentonite clay, may be used as a rheological additive to improve the ultra-low shear rate viscosity of oil-based or synthetic oil-based drilling fluids (O/SBMs) and to increase the carrying capacity of the oil mud, while reducing the high shear rate readings. The clays are modified by treating them with quaternary amines and/or quaternary ammonium salts. The organophilic clay mixture significantly yields stable gels that are non-progressive compared to each individual organophilic clay used separately.