The addition of self-MSBO (metathesized soybean oil) to biodiesel significantly depresses the onset temperature of crystallization (T-on). MSBO and self-MTO (metathesized triolein), used as model systems, were separated into their constituent "molecular families" using column chromatography and crystallization fractionation and tested as crystallization modifiers of biodiesel. The results indicate that cis-unsaturation combined with a straight chain moiety is a critical structural architecture for disrupting biodiesel crystallization. The data obtained with TAGs (triacylglycerols) propose that the most effective stereospecificity is when the two fatty acids in the cis-configuration are in the sn-1 and sn-3 positions and a trans-/saturated fatty acid is at the sn-2 position. The conversion of cis-double bonds to trans double bonds by self-metathesis explains the lowering of T-on of biodiesel. The fractionation of MSBO, leading to a liquid fraction enriched with molecules having cis-unsaturated fatty acids out-performed MSBO in lowering T-on of biodiesel. This knowledge can be used for the design of economical and more functional materials from MSBO and other metathesized vegetable oils using selective and practical fractionation methods. The findings of the study suggest that the use of biodiesel with significant saturated methyl ester content can be extended in colder months of the year. (C) 2015 Elsevier Ltd. All rights reserved.