PURPOSE: To provide an emulsifier composition useful for boring and maintaining a well and to provide an emulsion composition containing the emulsifier composition.

CONSTITUTION: This emulsifier composition comprises an emulsifier containing benzene-soluble solid organopolysiloxane resin copolymer, a hydrolysis-resistant compound which has at least two organopolysiloxane-polyoxyalkylene molecules connected with hydrolysis-resistant cross-linking group, a polydiorganosiloxane- polyoxyalkylene copolymer having at least one long chain alkyl group and at least one polyoxyalkylene group in the same molecule, and a polysiloxane- polyoxyalkylene copolymer surfactant. The emulsion composition is comprised of a brine, a liquid hydrocarbon and the emulsifier composition.