Prediction of volumetric biodiesel/petrodiesel blend ratio (V-BD) 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 (<15 ppm S) diesel (ULSD) fuels and SG at 15.6 degrees C was measured. Least-squares statistical regression on SG data from each of the biodiesel/ULSD blend sets revealed highly linear relationships (R-2 > 0.991) between SG and V-BD. Blends with the highest R-2 values from each of the ULSD fuels were used as model systems to develop predictive equations useful for calculation of V-BD from SG. The results indicated that accurate prediction of V-BD 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. Published by Elsevier Ltd.