The experiment under lab condition was conducted to investigate the effect of petroleum hydrocarbon contamination on soil microorganisms and biodegradation. The experiment was conducted in 12 treatment and three replication. The treatments include soil contaminated with Kerosene, Diesel, lubricate oil and used lubricate oil in three concentration 0%, 5%, and 10%. contamination with hydrocarbons significantly decreased the count of heterotrophic bacteria and there was reversal relationship

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... n the contaminant concentration and the count of heterotrophic bacteria. The results indicated soil contamination with hydrocarbons significantly increased the count of Hydrocarbon Utilizing Bacteria (HUB). The effect of petroleum hydrocarbons on fungi count differed according to the type of hydrocarbons, concentration of contaminant and the periods of incubation. Our results show that soil contamination by hydrocarbons caused significant increase in actinomycetes count at all hydrocarbon types and concentrations except 5% used and non-used lubrication oil. The higher percentage of biodegradation in hydrocarbons contaminated soil 49.6% was recorded in soil contaminated with 5% kerosene while the lower percentag10.8% was recorded with soil contaminated 10% lubricate oil.