Mineral oil products are produced and utilized to a large extent. During the production, storage, filling up and utilization many spills occurred during the last decades. As a result, mineral oil contamination is recently one of the main problems in soil remediation. The predominant portion of the different oil components is easily degradable by microorganisms. But, its biodegradation in natural environments is often limited by the availability of the substrate to the microorganisms or by limited concentrations of nutrients and electron acceptors. Thus, the optimization of the environmental conditions can significantly improve the efficiency of degradation in both soil and groundwater (Enhanced Natural Attenuation approach). One major limiting factor in terms of the bioavailability of mineral oil is its limited solubility in water. Enhancing the solubility of the contaminants e.g. by the use of surfactants can significantly improve the efficiency of biodegradation. But, for the purpose of bioremediation only those surfactants should be used that are themselves completely biodegradable. Moreover, they have to be compatible to the surfaces of the bacteria. These requirements are met by biosurfactants and by those surfactants that contain structures comparable to naturally occurring microbial surfactants. The efficiency of such a close-to-nature surfactant (BioVersal FW) has been demonstrated for the in situ remediation of a highly contaminated site at Halle/S. (Germany). During the field scale investigation up to 50 g hydrocarbons per kg soil were eliminated over a period of 15 months.