The major drilling problems such as fluid loss, wellbore strengthening, well control, carrying capacity, torque & drag, stuck pipe, etc. can result from the improper matching of drilling fluid properties. These problems occur due to variations in pressure, and temperature which has a great impact on the rheological properties. Drilling fluid properties can be modified for the successful drilling operation. Research continues the development of drilling fluid in shale inhibition, rheology modification, wellbore strengthening, high-temperature, high-pressure (HTHP) drilling fluids, etc. The main goal of this project is to develop a rheology-based pressure drop calculation incorporating the effects of temperature, pressure and gel strength of drilling fluid using experimental results for the better understanding of undesirable viscosity fluctuation and pressure losses. This study is based on the hypothesis that the rheology model for pressure loss prediction can be investigated to the desired level in an experimental laboratory facility, which can be applied to solve/reduce drilling problems in wells. This study presents a simplified procedure for selecting the rheological model which best fits the properties of a given hydraulic fluid to represent the shear-stress, shear-rate relationship for a given fluid. The project assumes that the model which gives the lowest absolute average percent error (EAAP) between the measured and calculated shear stresses is the best one for given drilling fluid. The results are of great importance for achieving the correct pressure drop and hydraulics calculations. It is found that the API rheological model provides, in general, the best prediction of rheological behaviour for the mud samples considered (EAAP= 5.84%). API hydraulics calculation gives a good approximation to measured pump pressure within 14% of measured field data.