TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The hindered phenol is selected from 4-methyl-2,6-di-tert-butylphenol; 2,4,6-tri-tertbutylphenol; 2-methyl-6-tert-butylphenol; 2,4-dimethyl-6-tert-butylphenol; 2-tert-butyl-4,6-dimethylphenol; 2,6-di-tert-butyl-4-ethylphenol and 2,6-di-tert-butyl-4-n-butylphenol. The mixture (b) has a ratio of aromatic amine i) to hindered phenol ii) of 1:1 (preferably 1:1-4:1) wt.%; has a ratio of aromatic amine i) to hindered phenol b) of 1-1 (preferably 1:1-4:1) wt.%. The aromatic diamine of the mixture b) is a blend of N-(1,4-dimethylbutyl)-N'-phenyl-1,4-phenylenediamine and N-(1,3-dimethylbutyl)-N'-phenyl-1,4-phenylenediamine), and the statically hindered phenol of the mixture b) is 2,6-di-tertbutyl-4-methyl phenol. The mixture b) is present in the biodiesel fuel in an amount of 1-10000 ppm. The mixture b) is present in the biodiesel fuel in an amount of 1-10000 (preferably 50-5000, especially 100-2000) ppm. The biodiesel fuel comprises methyl esters of soybean oil, mustard seed oil, rapeseed oil, canola oil or tallow. Preferred Composition: The composition further comprises at least one other component selected from dispersants/detergents, octane improvers, carrier fluids, demulsifiers, antifoam agents, anti-icing additives, biocides, combustion improvers, alkali or alkaline-earth metal detergents, drag reducers, metal deactivators, lubricity additives, dyes, markers, odor masks, odorants and stability improvers. EXAMPLE - A composition was prepared as follows: Mixture (1:1 wt.%) of NL 420 (RTM: N-phenyl-N'-alkyl-p-phenylenediame) which comprised a blend of 12-88% N-(1,4-dimethylbutyl)-N'-phenyl-1,4-phenylenediamine and 88-12% N-(1,3-dimethylbutyl)-N'-phenyl-1,4phenylenediamine) and 2,6-ditertbutyl-4-methyl phenol (BHT) added to rapeseed-ME (methyl ester of rapeseed oil (RME)) biodiesel at a treat rate of 1000 ppm (w/w). The synergistic antioxidative effect of N-phenyl-N'-alkyl-p-phenylenediame (NL 420) and 2,6-ditertbutyl-4-methyl phenol was demonstrated by an inducement time of 28.2 minutes, 6.4% and 19.5% increase. The synergistic blend gave an increase of induction time equal to a (28.2-25)/25x 100=12.8% improvement.