Vacuum residuum was upgraded in an ultrasonic reactor of our own design. We found that during sonication in the absence of a hydrogen donor, the viscosity of the vacuum residuum is reduced by 10.98%; without sonication but in the presence of tetralin, it is reduced by 30.9%; and with combined tetralin treatment and sonication, the viscosity is reduced by 39.27%. The synergistic effect of ultrasound and tetralin results in a product with more stable viscosity, higher percentage of light components, lower density and lower pour point than obtained by separate application of these technologies.