1. n. []

An outdated distinction between two types of oil muds. In the past, invert-emulsion oil muds were those with more than 5 vol.% emulsified water, and oil-base muds were those with less than 5 vol.% water. Today, this distinction is not pertinent because the general term oil mud covers all water concentrations.

See related terms: asphalt,  emulsion,  fatty-acid soap,  hectorite,  interfacial tension,  invert emulsion,  mud,  oil content,  oil mud,  oil-base mud,  oil-in-water emulsion,  oil-mud emulsifier,  organophilic clay,  organophilic lignite,  rheology modifier,  surface tension,  synthetic-base fluid,  synthetic-base mud,  water-in-oil emulsion