Discloses environmentally friendly, low temperature base oils and drilling fluids, or drilling mud compositions useful in the production of oil and gas. The drilling fluid is constituted of one or more of weighting agents, emulsifiers, wetting agents, viscosifiers, fluid loss control agents, proppants, and other particulates such as used in a gravel pack, emulsified with a paraffinic solvent composition which forms a continuous oil phase, or water-in-oil invert phase. The solvent composition is constituted of a mixture of C.sub.10- C.sub.24 n-paraffins and isoparaffins having an isoparaffin:n-paraffin molar ratio ranging from about 0.5:1 to about 9:1, the isoparaffins of the mixture contain greater than 30 percent, preferably from about 30 percent to about 50 percent, of mono-methyl species, and greater than 30 percent, preferably from about 30 percent to about 50 percent of multi-methyl branched species and isoparaffins which contain one or more branches of carbon number higher than methyl, based on the total weight of the isoparaffins in the mixture. The presence of the mono-methyl species is sufficient to provide the admirable environmentally friendly qualities, and the multi-methyl branched and isoparaffin species more highly branched than methyl provide low temperature properties.