Aqueous structured surfactants, e.g., lamellar, or preferably spherulitic systems optionally containing suspended solids are used as functional fluids, such as drilling fluids, cutting fluids, hydraulic fluids, heat transfer fluids, construction muds and lubricants. A composition consisting essentially of: water; a surfactant or mixture of surfactants present in a concentration sufficient to form a mobile spherulitic or dispersed lamellar phase in the absence of an electrolyte; and a substantially water insoluble functional material, suspended in the composition, the composition being substantially free from electrolyte.