Aged drilling wastes were remediated under lab. and pilot plant conditions. An enrichment of the wastes in microbial species of autochthonous microorganisms resulted in decrease in contents of petroleum-derived contaminants from 200 g/kg dry mass to an acceptable level of 998 mg/kg dry mass. A low content of contaminants and a lack of soil toxicity after purifn. were proven by phys., chem., chromatog. and toxicolog. analyses.