Abstract: The microbial decontamination of soils contaminated with hydrocarbons, in particular with mineral oils, by microbial oxidation is improved by a process in which in addition to supplying the oxygen necessary for degradation, by aeration, soluble nutrients, water and soluble or dispersed biosurfactants as such or mixed with chemical surfactants are metered into the contaminated soils directly or into the removed contaminated soil layers, in one or more batches at time intervals, in an amount such that the formation of toxic intermediates which slow down or block microbial degradation in prevented, the accessibility of mineral oils and their products for the microorganisms is simultaneously increased and, as a result, accelerated, virtually complete mineralization by respiration to CO.sub.2 and H.sub.2 O is effected.