An aqueous suspension used in rotary drilling. Mud is pumped down through the drill pipe and up through the annular space between it and the walls of the hole. The most common bases of drilling muds are bentonite, lime, and barite in a finely divided state. The mud helps remove cuttings, prevent caving, seal off porous zones, and hold back formation fluids. Oil-based muds (inverted muds) are sometimes used; they generally are nonconductors of electricity.