This invention relates to an improved oil-base drilling fluid composition and its use. The improved oil-base drilling fluid composition of this invention is characterized by thixotropic properties which result in a yield point of at least 4.0. The composition includes an oil-base continuous phase and a gelling composition. The gelling composition includes a latex material in combination with one or more functional monomers selected from the group consisting of amides, amines, sulfonates, monocarboxylic acids, dicarboxylic acids and combinations thereof and wherein at least one of the monomers includes a nitrogen containing material.