1. n. [Drilling Fluids]

The pressure that must be applied to the low-salinity side of an osmotic system to prevent water movement into the high-salinity side by osmosis. Conversely, it is the suction pressure that a high-salinity system exerts on the low-salinity system across a semipermeable membrane in an osmotic system.

See: activity of aqueous solutions,  methylglucoside drilling fluid,  osmosis