In contrast to most other petroleum products, lube oils are not used up completely in the machinery or mechanism, and after a certain interval of time are drained as 'used', i.e., oil that has partially or completely lost its service qualities. In the last decade, considerable attention throughout the world has been given to the rational utilization of used petroleum products. This change has come about in part because of economic considerations (higher prices for petroleum crudes and products) and in part because of ecological considerations related to the ever-increasing pollution of the environment and increasingly stringent demands for environmental protection.