It is very important to design a stable mud system for any detailed drilling programs. Application of the best practices and well planned engineering field execution is critical in drilling and completing HPHT wells in a cost effective manner and minimal operational problems. Conventional mud designs and test equipment fell short of addressing the inherent problems associated with HPHT wells. In this study, the conventional practices in mud design were reviewed and advances in design for best practices developed for Mafia field. Many of the conventional practices were actually found to be inadequate for HPHT drilling. This paper present techniques on determining and applying mud properties at HPHT deep wells through a rigorous laboratory test and mathematical equations to generate detailed engineering guidelines for HPHT drilling fluid. Water based mud were formulated with special additives at temperature between 250-500°F and 5,000-10,000 psi to check for its stability under such elevated temperature and pressure. A standard temperature concept used for controlling the surface mud weight was defined. With the actual field results from the Mafia field, model equations were developed and the sensitivity analysis done to show the relative influence of pressure and temperature on the drilling fluids using the spider and tornado plots. The model equations derived from the multiple regression analysis were used to predict and rank the best rheological properties for the field, thereby saving the time and rigors associated with laboratory experiments.