Diesel fuel is currently showing the most rapid growth rate of all petroleum fuel products and is projected to maintain this well into the 1980's. Middle distillates production in Canada has always been high because of heating oil requirements, resulting in a gasoline to middle distillate ratio of 1:1. This ratio is expected to continue despite a decrease in the heating oil market because of the predicted increase in the diesel fuel market.In order to provide the volume needed for future diesel fuel demand there will have to be a drop in initial boiling points, an increase in final boiling points as well as the use of more cracked stocks. Canada is also faced with the refining of synthetic crudes which currently represent about 10% of crude production. These produce middle distillates with low cetane numbers.In order to overcome the problems created by these changes, we see the increased use of cetane improver additives to raise the cetane number of the diesel pool and the use of flow improver additives to enable higher cloud distillates to be used. As diesel fuels are being blended closer to the minimum cetane requirements, there is a need for better techniques for the monitoring of cetane number.