Biodiesels and biomass EtOH are currently considered the most applicable and essential biomass fuels. Furthermore, MeOH and BuOH are also attracting attention as alternatives. These fuel types can be used to reduce exhaust emissions from gasoline engines because they are renewable oxygenated bioresources. Three biofuel additives, namely, MeOH (10%, M10), EtOH (10%, E10), and BuOH (10%, B10) were used to compare the engine performance properties and exhaust gas emission levels upon combustion of mixed biomass fuels and pure petroleum fuel (clean unleaded gasoline, E0). The engine combustion temperature dropped by 4.32%, O-2 emission increased by 6.67%, NOx emissions decreased by 13.46%, CO emission decreased by 44%, and hydrocarbon emissions fell by 29% if biomass fuels were used. Therefore, mixed biofuel additives and gasoline could substantially reduce engine exhaust emissions, including oxides of C and N, hydrocarbons, etc., because the biofuels contain higher oxygen contents that facilitate complete combustion.