1. n. [Drilling Fluids]

An emulsion in which oil is the continuous or external phase and water is the internal phase. Invert emulsion usually refers to an oil-base mud, and the terms are considered synonyms. Invert-emulsion muds can be run with 5 to 50% water in the liquid phase, although there are systems that are 100% oil.

See: emulsion mud,  interfacial tension,  invert-emulsion oil mud,  oil-base mud,  surface tension