Oil extraction from oil sludge with biosurfactant formulas was optimized by a Taguchi orthogonal array design of L16 (4(5)) with five main factors, including biosurfactant type (surfactin, lichenysin, rhamnolipid and emulsan), biosurfactant concentration, pH, salinity and solvent. Oil recoveries obtained with the sixteen batch washing experiments with the selected levels of each factor were processed with Design Expert/SPSS and a specific combination of factors with a predicted oil recovery of 76.81% was obtained. The predicted optimal biosurfactant formula of 2.0 g/L rhamnolipid, pH 12.0, 10 g/L NaCl, and 5.0 g/L n-butanol were validated by a washing experiment that yielded an oil recovery of 74.55%, which was 27.28% higher than the grand average oil recovery of the whole experiment design. Based on the optimum biosurfactant formula, the oil extraction process followed first-order kinetics as the washing rate constant and final oil recovery increased with temperature. These results will be informative and meaningful for the design of oil sludge treatment in industrial application. (C) 2012 Elsevier Ltd. All rights reserved.