Parametric Tests Characterize Additive Performance in a Blend: A combination of different anti-oxidation additives may produce higher oxidation stability than a single additive. If this is true, the proportion of additives blended with biodiesel fuel can be reduced. However, depending on the additive types, the effects may or may not be expected, and it is not clear what combination of additives is appropriate to increase oxidation stability as intended. Researchers at Shiga Prefecture University and Seiko Chemical conducted parametric tests to characterize the additive performance with a blend of two additives. In general, such anti-oxidation additives as phenolic and amine additives were combined to maintain the detergency of engine lubricating oil. Thus, these additives were combined to evaluate the feasibility of improving oxidation stability of soybean methyl ester. This chapter reports various test results and the characterization of oxidation stability.