Prediction of volumetric biodiesel/petrodiesel blend ratio (VBD) from specific gravity (SG) data was the subject of the current investigation. Fatty acid methyl esters obtained from soybean, palm and rapeseed oils along with chicken fat (SME-1, SME-2, PME, RME and CFME) were blended (0–20 vol%) with three ultra-low sulfur ( 0.991) between SG and VBD. Blends with the highest R2 values from each of the ULSD fuels were used as model systems to develop predictive equations useful for calculation of VBD from SG. The results indicated that accurate prediction of VBD from SG was most effective when applied to blends prepared from the same fuel-types as the model systems used to develop the predictive equations.