The regulations on diesel engine emissions are growing worldwide. The use of cetane improvement additives in diesel fuels is a cost-effective option to reduce engine emissions and enhance engine operations.Cetane response, which may be defined as the relationship between the change in cetane number of the fuel and the concentration of the cetane improver, is a key factor for commercial acceptance of a cetane improver. A study of the cetane response of di-t-butyl peroxide in a variety of commercial U.S. No. 2 diesel fuels and in various diesel fuel blend stocks was performed. The performance of the peroxide has been directly compared to that of the traditional cetane improvement additive, 2-ethyl hexyl nitrate in these fuels. On an average, di-t-butyl peroxide was found to be 85% to 90% as effective as the nitrate. A correlation between the cetane response of both the cetane improvers with the different fuel properties is discussed. Predictive cetane response equations based on fuel properties, for both peroxide and nitrate, have been developed.