In this work attempt was taken to develop a method for improving the straight run refining process. It is established that the yield of main products petrol and diesel increases from 28.88% to 32.84% and 40.08% to 46.19% respectively when optimum quantity of additives was used. Maximum quantity of additives depends upon the type of additives that's why optimum quantities of additives used in this process of distillation are different for different additives. By TGA, 1H-NMR and GCMS analysis, it is established that the quality of products (octane number of gasoline which mainly depend upon the fractions of iso-paraffins and aromatics hydrocarbons and cetane number of diesel on straight chain paraffins etc.) also improved when optimum quantity of additives was used. This method mainly gives the opportunity to petroleum refiners to get their desirable quantity of petroleum products (petrol, diesel, lubricating oil and furnace oil) on the one hand and improve the quality of the products on the other hand.