Acid treatment is one of the cheapest techniques and least applicable processes in the recycling of used lubricating oils. In this work, the performance of sulphuric acid in the treatment used oil was studied. The effects of the critical treatment parameters (acid volume, concentration of the acid, treatment temperature, stirring time and treatment time) were investigated by varying one treatment parameter at a time and analysing metal content in the sample of the treated oil using atomic absorption spectrometry (ASS). Thereafter, an optimal solution was determined by the combination of the optimum values of each treatment parameters. The original conventional treatment parameter values, resulted in 13.2 ppm and thereafter was optimised to 11 ppm this showed a definite improvement in efficiency. This result is also comparable to other data obtained in previously studied work which employed the same conventional treatment parameters. The optimal solution is within 10% variation as compared the standard individual metal content which ranges 0-10 ppm.