It is known that native oil-degrading microorganisms are ubiquitous. They can be isolated from contaminated soils. In this study, biodegradation experiments were carried out to evaluate the efficiency of pollutant removal by adding the selected microorganisms. Five mixed cultures and 3 single bacteria strains, Pseudomonas sp., Arthrobacter sp. and Mycobacterium sp. were isolated from hydrocarbon-contaminated soils by enrichment on either crude oil or individual hydrocarbons, as the sole carbon sources. The strains were selected based on their ability to grow in medium containing crude oil, used engine oil or both. Their ability to degrade hydrocarbon contamination in the environment was investigated using soil samples contaminated with used engine oil. The mixed starter culture #1 degraded 66 % of aliphatic compounds in the engine oil, after 60 days of incubation. The mixed starter culture #5 removed 47 % of aromatic compounds during 60 days of incubation, which is the maximum efficiency among the starter cultures, in this study.