Abstract: The present invention relates to a surfactant for use in invert emulsion drilling fluids, the invert emulsion drilling fluid produced therefrom, and a method of drilling, completing and working over a subterranean well utilizing said drilling fluid. The drilling fluid comprises an emulsion formed by producing a diamide having from between about 20 mole percent and about 35 mole percent of a polyamine, and from between about 30 mole percent and about 70 mole percent of a fatty acid having from between about 6 to about 20 carbon atoms therein, the diamide thereafter being further reacted with from between about 15 mole percent and about 35 mole percent of a tricarboxylic acid. The total amine value of said oligamide being from between about 10 to about 30, and the acid value of said oligamide being from between about 26 to about 46. When the surfactant is diluted to about 70 w/w percent concentration with a suitable solvent, the ES.sub.