Storage stability is an important aspect in the commercialization of biodiesel. Due to the chemical structure of methyl ester, long-term storage may lead to the degradation of fuel properties that can make it difficult to meet the EN 14214 Standard. This paper examines the degradation of several biofuels (sunflower methyl esters, used cooking oil methyl esters and blends with commercial diesel) under different storage conditions over a 6-month period. The storage conditions simulated real-life conditions by using similar temperatures to those found in commercial tanks, with little air turnover and in the absence of light. Extreme temperature conditions were also studied to determine if this variable has an effect on storage stability. Opaque glass or stainless steel storage containers were used to check the interaction between metal and biofuel. The results show that temperature plays an important role in the degradation of methyl esters. On the other hand, stainless steel was found to be a suitable material for the commercial storage tanks as the effect of this material on stability was almost negligible. The blends with commercial diesel performed better in long-term storage. This was probably due to the effect of the ester dilution and the presence of additives in commercial diesel. (C) 2011 Elsevier Ltd. All rights reserved.