The capacity of aqueous biosurfactant solutions to remove ULO from contaminated sand was also investigated and compared with that of synthetic surfactants (sodium dodecyl sulfate SDS and tween 80) at several concentrations (fig. 4a) For SDS, the maximum ULO removal was attained at the CMC, namely, a removal of 69. For Tween 80 and biosurfactant, increasing concentrations enhanced the removal of ULO, increasing from about 67 at the CMC to about 88 and 92 at 5CMC and 10CMC, respectively (fig. 4a). The maximum percentage of oil removal by the biosurfactant and Tween 80 was around 4.4-fold higher than that of the negative control (distilled water; 21 oil removal). Two mechanisms are associated with the removal of crude oil from soil: mobilization and solubilization. Mobilization occurs at concentrations below the CMC, and the phenomena associated with this mechanism include the reduction of surface and interfacial tension. Solubilization occurs above the CMC of the surfactants, as the apparent solubility of oil increases dramatically due to aggregation within the surfactants’ micelles (Urum and Pekdemir 2004)