Factors affecting oxidation stability for several commercially available biodiesels were primarily investigated by acid value (AV) and induction period (IP) evaluations in this study. It was found that the measured IP at different storage time points were somewhat dependent on the saturated degree of fatty acid methyl esters (FAMEs), the corresponding measured AV scattered randomly. Generally, AV increased and IP decreased after one year of storing in a dark cold room in an air-tight tank. Solvents (methanol, acetone and water) did not show a contribution to altering IP. Metals (copper and lead) showed the strongest detrimental effects to oxidative stability although somewhat depending on the particle size and oxide coating thickness, however, aluminum alloy and steel were not the case. Among the antioxidants, pyrogallol (PY) was the best in enhancing IP with a concentration of less than 3000 ppm, however, tert-butylhydroquinone (TBHQ) was the best after 3000 ppm, followed by propyl gallate (PG), butylated hydroxyanisole (BHA), 3,5-di-tert-butyl-4-hydroxyltoluene (BHT), and alpha-tocopherol. The appropriate dosage of PY was also evaluated to achieve the specified IP regulated by EN-14112 for samples with copper or lead contamination. (c) 2012 Elsevier B.V. All rights reserved.