The practice of using hollow glass microspheres to reduce the density of drilling fluids and cement slurries has become more prevalent in recent years due to increasing demand for "hydrostatic pressure management" with high performance low density cement and fluids. The use of hollow glass microspheres in drilling fluids presents unique benefits and challenges. This paper addresses a case study of a recent offshore managed pressure drilling project which ONGC conducted using glass bubbles in the Mumbai High. The study demonstrated the value of bubbles as a mud density reducer in a challenging drilling environment and also showed the importance of specific operational parameters in the project's success. A subsequent field study was conducted to quantify, under controlled conditions, the impact of these parameters on the bubbles performance while drilling. Mud density and mud solids content were monitored as flow rate (FR), weight on bit (WOB) and drill string rotation speed (RPM) were changed. The tests were conducted at the GTI Catoosa Test Facility rig under the co-direction of 3M and Newpark Drilling Fluids. A new generation of glass bubble, with a density of 0.42 g/cm3, an isostatic compressive strength of 8000 psi, and a smaller particle size was selected for this work. Solids control equipment settings were shown to be one of the key components to success in this experiment. A comprehensive mud sample collection plan enabled the monitoring of mud density, solids content and rheology parameters versus time. This study confirmed that glass bubbles can be used to satisfactorily maintain the mud density within an acceptable range in an economical way. The glass bubbles, specifically the new generation with a higher strength to density ratio, were shown to be an efficient, convenient, and sustainable way to reduce the density of a drilling fluid.