Sagging of particles is one of the most critical issues when drilling deep oil and gas wells especially when the hole angle is greater than 30 degrees. Accumulation of cuttings at the bottom of the hole around the drilling bit as a result of barite sagging cause severe problems such as the loss of well control. Temperature has a major effect on barite sagging so there is a need to develop a new drilling fluid formulation that can prevent barite sagging under different geometries of hole path and high temperatures (greater than 300 degrees F). The objective of this study is to evaluate the effect of using an organophilic phyllosilicate (OP) as an anti-sagging additive to prevent barite sagging in an invert emulsion drilling fluid (IEDF) at high temperature (350 degrees F). Static sag tests were conducted at vertical and inclined (45 degrees) positions at 350 degrees F. Dynamic sag tests were performed at 120 degrees F. The second objective is to determine the optimum concentration of OP and evaluate the effect of the selected concentration on the rheological and filtration properties of the IEDF at 350 degrees F. The results show that the optimum amount of OP for preventing barite sagging at 350 degrees F in both vertical and inclined positions is 1.5 g. Adding 1.5 g of the OP prevents barite sagging under dynamic conditions and enhances the theological properties by increasing the yield point plastic viscosity ratio. The OP enhances the suspension capability of the drilling fluid at low shear rate (3 rpm). (C) 2019 Elsevier B.V. All rights reserved.