The lubricity of ultra-low sulfur diesel (ULSD) and synthetic fuel (S8) blended with different levels of cotton seed oil, soybean oil, or poultry fat based biodiesel was evaluated using a high-frequency reciprocating rig (HFRR). The lubricity of ULSD and S8 blends increases sharply as the biodiesel blending level increases and then levels off at similar to 2 vol %. The effects of individual minor components of biodiesel, free fatty acids (FFAs), glycerol, antioxidants, phospholipids, and water, on lubricity enhancement of ULSD were investigated. Among the minor components, polar compounds achieved better lubricity improvement. The order of the effect was FFA > soy biodiesel > phospholipids > antioxidant > glycerol > distilled soy biodiesel > individual FAME. Lubricity of the residues of distilled cotton seed oil and yellow grease biodiesel was also compared to the distillates. The effect of the temperature with 2 vol % soybean oil (SBO) blend with ULSD was examined. This biodiesel mixture shows better lubricity, attributed to boundary film formation, at temperatures greater than 70 degrees C.