In this study the biodegradability of asphaltenes was investigated using four bacterial consortia isolated from oil contaminated soils and sludge. The species in consortium 1 were identified as Pseudomonas aeruginosa and Pseudomonas fluorescens. Consortium 2 contained Citrobacter amalonaticus and Enterobacter cloacae. Consortium 3 contained only one species identified as Staphylococcus hominis, and the species in consortium 4 were identified as Bacillus cereus, and Lysinibacillus fusiformis. Spectrophotometry at 281 nm wavelength was applied to quantify asphaltenes biodegradation. The biodegradation tests were performed in flasks with the initial asphaltenes concentrations of 2, 4, 10, 20, 30 and 35 g/L for the four consortia. Under shaking conditions the best results were obtained with the initial asphaltenes concentration of 35 g/L. With this initial concentration, consortia 1,2,3, and 4 were able to degrade 51.5%, 43%, 21.5% and 33.5% of asphaltenes, respectively at 40 degrees C in two months. Under static conditions the best results were obtained with the initial asphaltenes concentration of 30 g/L. Under these conditions, consortia 1,2,3, and 4 were able to degrade 32%, 27%, 15%, and 24% of asphaltenes, respectively at 40 degrees C in two months. Kinetic studies showed that Tessier model could accurately describe asphaltenes biodegradation under shaking conditions. Kinetic parameters of the model were fitted by the method of Differential Evolution Optimization using a specific set of experimental data for each consortium. FT-IR analysis showed that alkene and alkyne functional groups were easily biodegradable while aldehydes resisted biodegradation. (C) 2013 Elsevier Ltd. All rights reserved.