Publisher Summary About half of the industrial and nonindustrial oil processes have led to an industrial application. Some of them appear very similar, the difference being in the process implementation or in the use of additives often progressively perfected and patented. This chapter describes the different processes that exist on the market. Every process generally comprises of a series of successive treatments: thermal treatment, vacuum distillation, deasphalting, catalytic treatment, and bleaching on clay. For these different processes, the inlet feedstock is waste engine oil, relatively constant in quality if the collection is done correctly. The objective is to obtain base oil divided into fractions of different viscosities to get marketable lubricants after blending with additives. Three cases are considered and sections of the process are described.