The invention discloses a compounded hydrocarbon oil which comprises a base hydrocarbon oil, preferably a mixture of paraffinic hydrocarbons, propylene carbonate, and a liquid fatty acid containing at least 12 carbon atoms per molecule, preferably tall oil fatty acid. The volume ratio of propylene carbonate to liquid fatty acid is from about 3.5 to 1 to about 7 to 1. Preferably the concentration of propylene carbonate is from about 0.002 gal/gal oil to about 0.0057 gal/gal oil and the concentration of the liquid fatty acid is from about 0.0003 gal/gal oil to about 0.0015 gal/gal oil. The invention further comprises a method of compounding the compounded hydrocarbon oil and an oil base drilling fluid prepared from the compounded hydrocarbon oil. Preferably the compounded hydrocarbon oil is characterized by an increase in the low shear rate viscosity of the oil of at least 5,000 centipoise or mixing 7.5 lb/bbl of an organoclay therein.