Interest in higher cetane quality for automotive diesel fuels is increasing worldwide because of the emissions benefits high cetane quality offers. Cetane quality has for many years been measured using the ASTM D613 CFR engine test procedure. Unfortunately, this technique is of relatively poor precision but, as presented here, testing strategies can be employed which permit enhanced measurement precision, with no increase in test time.Interest in the benefits of cetane number improver additives (CNIs), especially 2-ethylhexyl nitrate (2-EHN), as a more cost effective route to enhanced cetane quality compared to refinery processing is also increasing. Associated with this, is the growing need for prediction equations which relate final cetane quality to fuel properties and additive use. Mathematical relationships involving base fuel cetane quality are shown to predict final cetane quality with enhanced precision when compared to previously reported prediction equations using other fuel parameters.Work has also been carried out to investigate cetane number increases with the peroxide based cetane improver additive di-tertiary butyl peroxide (DTBP), in a range of base fuels, from which performance and prediction relationships compared to 2-EHN have been developed. This paper explores the use of a combination of these cetane enhancing additives.