NOVELTY - Biocide composition comprises: (a) water; (b) at least one biocide comprising (i) a halogen substituted xylenol compound, (ii) a phenolic compound, (iii) an antimicrobial natural or essential oil, and/or (iv) an antimicrobial component from natural or essential oil; (c) at least one surfactant, where the surfactant is anionic surfactant, amphoteric surfactant, nonionic surfactant, and/or their blends; and (d) at least one solubilizing agent.    USE - The biocide composition is useful: for treating water from oil and gas drilling operations; for treating an aqueous ore processing slurry; in a hydraulic fracturing fluid for fracturing subterranean formations (all claimed); for producing paper, wood, pulp, kaolin clay and/or their products that require control of microorganisms; in the polymer, films, porous and nonporous structures to prevent the growth of microorganisms; and as additives to water-based solutions, such as in latex paints to control undesirable properties such as odor, staining and discoloration due to microorganisms.    ADVANTAGE - The biocide composition is capable of effectively controlling microorganisms even in the presence of high salt content water and at high temperatures, and can be prepared in a safe and environmentally friendly manner.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) producing a concentrated biocide composition, comprising mixing the ingredients (a)-(d) as above per se together to form an emulsion; and    (2) a hydraulic fracturing fluid for fracturing subterranean formations connected to or adjacent to a drilled well bore, comprising field water, the biocide, the surfactant, the solubilizing agent, at least one proppant, and optionally, one or more ingredients comprising oxygen scavengers, polymers, friction reducers, viscosity modifier, corrosion inhibitors, pH adjuster, and/or metal chelate, where the biocide is present at a level of 5-5000 parts per million by weight of the hydraulic fracturing fluid.