Abstract: A process for enhancement of the cetane number of a diesel fuel which in one embodiment comprises:(1) treating a diesel oil with a nitrogenous treating agent in a nitrogen amount, equivalent on a 100% nitric acid basis, to about 10 weight percent or less of the diesel oil feed;(2) removing unreacted nitrogenous treating agent from the diesel oil of step (1) to produce a treated diesel oil, and;(3) blending the treated diesel oil of step (2) with an untreated diesel oil to produce a blended diesel fuel such that the added nitrogen content in the blended diesel fuel is(a) about 300 ppm or less of nitrogen added when the diesel oil treated in step (1) is obtained from virgin diesel oil stock; or(b) about 450 ppm or less of nitrogen added when the diesel oil treated in step (1) is obtained from hydrotreated diesel oil stock.