Free flow of fuels at reduced temperatures and the variation of their cloud point depending upon their source have been a concern that has not been addressed effectively. In this study we report MEL-A a biosurfactant as PPD to improve the low temp fluidity of biodiesel and hydrocarbon fuels at subzero temperature. MEL-A decreases the phase transition of biodiesel, consumer-grade diesel (CGD), and refinery-grade diesel (RGD) by 8.7, 3.3, and 10.3 °C, respectively. The addition of MEL-A decreases the cloud point of biodiesel, CGD, and RGD by 3.2, 9.0, and 1.5 °C. The mechanism of action of MEL-A is elucidated by studying the thermal behavior of individual fatty acid methyl esters and their mixtures as well as corresponding blends prepared. X-ray diffraction indicates that MEL-A interferes with the crystallization of methyl stearate, a major component of biodiesel. This interaction has been shown to be reversible and is mediated by its physical association with the fuel components. MEL-A is a biosurfactant, which makes it a sustainable and ecofriendly alternative to existing polymeric PPDs. © 2016 American Chemical Society.