A significant number of the wells operated by Esso Production Malaysia, Inc. (EPMI) utilize 12 1/4" production hole and have departure angles greater than 600. As a result of a detailed hole cleaning study, the oil-based drilling fluid was reformulated to reduce the plastic viscosity and yield point to obtain a lower rheology mud to improve hole cleaning. It was found that while the mud could be mixed with the low rheological properties, it could not be maintained effectively when reused over several wells. This finding led to an analysis and upgrading of the solids control equipment on the rigs. The study results that led to mud reformulation, the reformulation itself, and the subsequent solids control equipment upgrades are presented, along with the resulting improvements in drilling efficiency as well as the reductions in the residual oil remaining on cuttings.