This study purpose is to check a new technique in solvent extraction process on used lubricating oils using design of experiments (DOE) generated by MINITAB. In addition, study technique for decreasing the amount of N-Methyl-2-Pyrroidone used in the re-refining of used oil thus decreasing the operating cost of the extraction process. The experiments were done on pre-treated used lubricating oils, which was obtained from Alexandria Petroleum Company facility where light hydrocarbons and water were eliminated from it. Solvent extraction technique was done on the used lubricating oils using N-Methyl-2-Pyrrolidone (NMP) and butanol as a solvents. Different factors were studied by bench scale experiments such as: Solvent to solvent weight ratios, Solvent to oil weight ratios, mixing time, mixing speed and the extraction temperatures. A statistical analysis computer software (MINITAB version 17) was used to investigate those factors which affect the percent sludge removal from the used lubricating oils. Furthermore, the data obtained from both bench scale experiments and statistical analysis computer software shows that the most significant factors affecting the percent sludge removal from used lubricating oils was solvent-to-solvent weight ratios, while the least significant factor was the extraction temperature.