The biodiesel used in this work was produced in a pilot plant by basic methanolysis of crude palm oil using a methanol/oil molar ratio of 12:1, with 0.6% sodium hydroxide by weight as the catalyst. The reaction temperature and time were 60 °C and 1 h, respectively. The methyl ester composition of palm oil biodiesel (POB) was determined by gas chromatography (see Table 1). The commercial grade No. 2 diesel fuel (D) used had an elemental composition by weight of 87.2% carbon, 12.8% hydrogen and 0.0225% sulphur, and an aromatic content of 29.3% (13% monoaromatics, 13.3% diaromatics and 3% polyaromatics). Although several blends with a wide composition spectrum were prepared by splash blending [17], most of the tests were carried out with B5 (5% POB-95% D by volume) and B20 blends, due to their widespread use. Neat fuels are designated as B100 and B0, respectively. Blends were prepared on a volume basis at 25 °C. Although blend preparation on a weight basis has the advantage that weight fraction does not change with temperature, the common practice in the fuel industry is to carry out the mixing process on a volume basis at the ambient temperature of the blending location, usually a wholesale commercial plant. For this reason, the option selected in this work was to use blending rules as a function of volumetric fractions.