Petroleum substances are the main source of pollutants stored in old waste pits. They cause degradation of biological life in the area of storage. The aim of this article is to present laboratory research on petroleum pollutant biodegradation. The hydrocarbon contaminants in old drilling wastes came from the Graby-19 waste pit. The tests included basic bioremediation and inoculation with a biopreparation based on non-pathogenic species of bacteria and fungi, which were identified in molecular research. Multicriteria effectiveness estimation of petroleum pollutant biodegradation in the tested wastes enabled determination of a role of fungi in this process. Biopreparation enrichment was done in the final phase with non-pathogenic fungi isolated from the waste during purification. As a result, an increase in long-chain n-alkanes and aromatic hydrocarbon (BTEX and PAH) biodegradation was observed. Biodegradation rate constants for petroleum hydrocarbons, calculated on the basis of a mathematical model, can serve as proof of fungi usage in the bioremediation process.