The implementation of stringent diesel engine emissions regulations is growing worldwide. The use of high cetane diesel fuels is a cost-effective option that can be used to reduce engine emissions.A direct comparison of heavy-duty diesel engine emissions for three different low sulfur diesel fuels treated with di-t-butyl peroxide and 2-ethylhexyl nitrate, at the same cetane level, were evaluated. Both the peroxide and the nitrate cetane improvement additive significantly reduced all regulated and unregulated emissions including the oxides of nitrogen (NOx) emission. Di-t-butyl peroxide shows a small advantage over ethylhexyl nitrate in reducing NOx in all the three fuels. Compatibility of the peroxide and the nitrate additives, when mixed in a fuel blend, has been demonstrated by cetane response and engine emissions for the fuel blend.