Additive for oil-based drilling fluids

The present invention relates to an additive for improving the properties of an invert emulsion comprising water or brine in an oil or synthetic based drilling fluid for use in drilling a borehole in a subterranean formation, said additive comprising a wetting agent and a product produced by the Diels-Alder reaction of dienophiles, selected from compounds or reagents selected from the group consisting of carboxylic acids, polycarboxylic acids, acid anhydrides, and combinations or mixes thereof, with a mixture of fatty acids and resin acids derived from the distillation of crude tall oil, wherein said acid mixture comprises a ratio of fatty acids to resin acids ranging from about 4:1 to about 1:1, and wherein the ratio of said wetting agent to said product ranges from about 1:5 to about 1:1.