The intensive use of oil products is one of the most significant problems of environmental pollution. They pollute water, soil, and air. For these reasons, the search for effective methods of oil biodegradation is very important for solving environmental problems. The research aimed to isolate and select oildegrading microorganisms and to investigate their effectiveness in oil-contaminated soil “ex-situ”. Using microorganisms isolated from the contaminated soil, a biopreparation was developed consisting of bacteria, yeast and filamentous fungi. Microorganism isolates were identified using MALDI-TOF mass spectrometry (Bruker, USA). The biopreparation was tested in the soil treatment sites of GVT LT, Ltd (Kiškėnai village, Dovilai eldership, Klaipėda district) in two test variants. The count of microorganisms (CFU/g) in the soil was determined at the beginning of the research, after two weeks and every month thereafter until the end of the cleaning season by serial dilution method in media with 1% of diesel. The content of oil products (g/kg) was determined with the same periodicity according to LST EN ISO 16703. An effective biopreparation for the degradation of oil hydrocarbons has been developed. Within 5 months, it reduced the amount of oil products to 61,7% in variant No. 1 and 58,7% in variant No. 2.