Several commercial catalysts were tested for their activity for upgrading waste lubricating oils. The feedstock was vacuum distilled to remove the light and the heavy ends. Two trickle-bed reactors placed in series were employed, the top reactor contained a high surface area alumina and the bottom reactor the catalyst. A Ni-Mo-AI2O3catalyst was selected for further study on the basis of its higner activity and activity maintenance. Several different hydrogen pressures, reactor temperatures, and liquid volume hourly space velocities were employed to arrive at the most optimum process conditions. This paper will discuss the effect of catalyst and process conditions on the product liquid color, viscosity, nitrogen, and sulfur content.