Toxic lead additives to gasoline are no longer used in many countries worldwide. The principle objectives of the present work are to upgrade the quality of some petroleum products through various operations. This study investigated the effect of alternative additives such as Methanol, MTBE on the 80 RON gasolines, light and heavy Naphtha via different blends of variable percentages.  The CFR engine was employed to measure the Octane number of the produced blends while mixtures of other alternative additives were prepared and added to the previously mentioned blends. The obtained results showed that the additives have led to a significant improvement of the measured octane number of gasoline. Nevertheless, it was noted that decreasing the Methanol percentage had a negative effect on the environment. As illustrated by the results, it is noted that the gain in the research octane number in the methanol blended samples is higher than base gasoline. Also, the gaseous emissions produced on combustion such as carbon monoxide, nitric oxides and unburnt hydrocarbons have shown a noticeable decrease of 26% for unburnt, 16% for CO and 14.5 % for NOx. However, Carbon dioxide emissions have increased by 5.6 % which may are attributed to the complete combustion of the fuel on the expense of Carbon monoxide emissions. Moreover, the effect of oxygenate addition on the volume of air required to was detected in the decrease in the NO_x emissions.