Fluid-loss control is an important property of drilling muds that affects drilling operations in a number of ways. Three critical mud components are required to achieve extremely low fluid loss: fine day, emulsion droplets, and partially soluble additives such as gilsonites or certain polymers. By optimizing the mix, high-pressure/high-temperature (HP/HT) fluid-loss values as low as 0.1 ml/30 min at 120degreesC have been achieved.