The compatibility of biodiesel blends with five common elastomers (acrylonitrile rubber or NBR, fluorocarbon, neoprene, ethylene propylene diene monomer or EPDM, and silicone) was assessed using Hansen solubility parameters. A solubility analysis was performed over the full diesel blend range and the model used methyl hydroperoxide, acetaldehyde, and formic acid to represent the decomposition products of biodiesel. An empirical study was also conducted to determine the efficacy of the approach to predict the volume swell of elastomers. This study included the influence of biodiesel with acetaldehyde and formic acid. The solubility model showed good agreement with measured volumes for fluorocarbon, neoprene, EPDM, and silicone. However, solubility curves for NBR did not reflect the measured volume changes, and therefore the solubility parameters used for NBR in this study are not considered reliable. The results showed that formic acid caused higher swelling in NBR, fluorocarbon, neoprene, and silicone than did acetaldehyde. For EPDM, the measured volume decreased with both biodiesel concentration and the addition of formic acid.