A direct comparison is made between a peroxide based cetane improvement additive and the conventional cetane improvement additive, 2-ethylhexyl nitrate. The relative cetane performance of the two additives in two low sulfur fuels has been determined. The engine emissions from fuels containing each two of the additives have been investigated using a low emissions, Detroit Diesel Corporation (DDC) Series 60 engine. The oxides of nitrogen emissions for the peroxide containing fuel were found to be lower than those from the nitrate containing fuel. Peroxides are typically associated with having a detrimental effect on fuel quality. This issue has been addressed in terms of how this peroxide effects the carbon residue, oxidative stability, and elastomer compatibility of the fuel. The temperatures to which fuel is exposed in the injectors is increasing with the new low emissions engine designs. As a result of these increasing temperatures, the thermal stability of fuel additives is of increasing importance. The thermal stability of the peroxide is addressed.