The enzymatic hydrolysis of urea contained in an oil-displacing composition by the action of plant urease has been studied. Optimal ratios of urea to natural urease-containing sources have been determined for the intense hydrolysis accompanied by the release of CO2, which reduces the viscosity of crude oil, and ammonia, which forms an alkaline buffer system, thereby increasing the detergent properties of the composition. The effect of hydrolysis products on the rheological characteristics of heavy crude from the Usa oil-field has been examined. The recovery of viscous crude oil from a model reservoir using the oil-displacing composition and urease has been investigated. DOI: 10.1134/S0965544112060023