Optimization of process parameters for the regeneration of used mobil oil by acid/clay method using sulphuric acid as washing agent was successfully carried out. Used mobil oil was characterized before and after regeneration to determine the changes in the physicochemical properties of the oils. The viscosity, flash point and fire point of the oil increased after regeneration while the specific gravity and sulphur content decreased. The Atomic Absorption Spectrometry (AAS) carried out revealed the presence of eight different metals in the fresh mobil whose concentration increased during use but reduced after regeneration. The FTIR instrumentation analysis revealed that the used mobil oil has high concentration of some ester groups, aromatic materials, glycol and sulphur oxidation products while the proportion of these materials plunged significantly after treatment. Changes in the process conditions like acid concentration, settling time and bleaching temperature affected the effectiveness of the regeneration process by affecting the desired changes in the physicochemical properties. The process parameters were optimized using Central Composite Rotatable Design (CCRD) of Response Surface Methodology (RSM), with the aid of design expert. The design, which use purity as the response of the experiment, considered three independent factors of acid concentration, settling time and bleaching temperature; and the effects of these factors on the response are significant since their P-values are less than 0.05. An optimum theoretical purity of 0.86 was obtained at 6.5mol/lit acid concentration, 5.5hours settling time and 95.5 °C bleaching temperature, which agreed excellently with 0.85 actual purity obtained at the same conditions. Therefore, the regenerated mobil oil at these optimal conditions is capable of meeting commercial expectations.