Technical Abstract: Biodiesel is an alternative fuel made from transesterification of vegetable oil or animal fat with an alcohol that has many attractive fuel characteristics. However, biodiesel is more prone than petrodiesel to start-up and operability problems during cold weather. The present study investigates effects on cold flow properties of mixing soybean oil fatty acid methyl esters (SME) with fatty acid esters derived from transesterification of soybean oil with medium- and branched-chain alkyl alcohols. Admixtures of SME with 0-100 vol% tallow fatty acid methyl esters and with n-propyl, isopropyl, n-butyl, isobutyl and 2-butyl soyates were analyzed for cloud and pour point (CP and PP). CP and apparent solidification point (SP = PP - 1) data were employed to construct temperature-composition phase diagrams for each admixture in SME. Soyates with branched-chain alkyl headgroup moieties were more effective in decreasing CP and PP (or SP) than those with straight-chain headgroups, compared to unmixed SME. An admixture of 65 vol% isopropyl soyate in SME decreased CP by more than 5C compared to unmixed SME. In contrast, the same admixture with n-propyl soyate decreased CP by only 1.9C. Furthermore, an admixture of 65% n-butyl soyate in SME decreased CP by only 2.6C despite having an alkyl headgroup with a larger molecular weight than for isopropyl soyate. Analogous results were observed from sub-ambient differential scanning calorimetry analysis performed on mixtures of pure mono-alkyl stearates in methyl oleate solvent.