Used oils are lubricating oils, which have become unsuitable for their proposed use. They may be recycled through the use of rerefining process to achieve useful products. Environmentally-conscious design of processes and products is increasingly viewed as an integral strategy in the sustainable development of new refining and chemical processes. This study compares the lubricating oil before and after treated oil with rerefining processes. A laboratory setup of dehydration, extraction and hydrotreating processes were established to rerefine used oil collected from different sources. A comparison of its product characteristics with untreated oil characteristics is introduced, the results showed that pour point increased from -21o C for used oil to -6o C for treated oil. Sulfur content was found about 3124.9 ppm for used oil and 90.4 for treated oil. Also, viscosity (at 70o C, cst.) and density (at 15o C, g/cm3 ) decreased from 30.73 and 0.897 for used oil to 9.44 and 0.855 for treated oil. This study concentrates on the investigation of energy and environmental benefits for used oil pertaining to its reuse through: (i) recovering the heating value of used oils in a combustion process and (ii) rerefining of used oil to produce fresh lube oil products. Also, the recycling used oil has been evaluated as a continuous phase in synthetic based mud instead of synthetic hydrocarbons for oil well drilling fluids. The rheological, filtration properties and electrical stability of the synthetic mud, which formulated with the recycle used oil, were studied and compared to the synthetic mud formulated with pure synthetic hydrocarbons (MR). The thermal stability of the mud were also tested and compared to the MR.