The growth of motor vehicles over the past five years has reached 8.63 % per year. The increasing number of vehicles has an impact on increasing fuel consumption. One alternative energy as another fuel currently being developed in motor vehicles is bioethanol. The addition of bioethanol will certainly change the fuel properties, the fuel will be more difficult to self-ignite so the pressure generated in the combustion chamber will be more consistent. The coefficient of variation (COV) represents the ratio of the standard deviation to the mean of a set of data, in this study in-cylinder pressure data (IMEP) is used. Based on previous research that discussed the analysis of emission gas and fuel consumption on SI engine fueled with low-grade bioethanol and oxygenated additive, the authors examined further to analyze the characteristic of gasoline-ethanol blend and oxygenated additive to COVIMEP and exhaust gas emissions of the various fuel mixture at variable engine speed were investigated. The results of the study show that gasoline-ethanol blend and oxygenated additive decrease variation in combustion pressure. It also reduces exhaust emissions; CO and HC are found to be reduced while CO2 and O2 increased as concentration increases.