Currently, the accidental releases of petroleum products are of particular concern in the environment. Hydrocarbon contamination is one of the major problems facing industrialized nations today resulting from the activities related to the petrochemical industry. Hydrocarbon contamination may produce toxic effects such as ecotoxicity and carcinogenic risk on the soil and water, and on the human body such as the central nervous system, liver, kidneys, heart, and so forth. The process of bioremediation has been defined as the use of microorganisms to detoxify or remove pollutants owing to their diverse metabolic capabilities and is also an evolving method for the removal and degradation of many environmental pollutants including the products of petroleum industry. It is believed that many indigenous microorganisms in water and soil are capable of degrading hydrocarbon contaminants. Bioremediation functions basically on biodegradation, transforming complex organic contaminants to other simpler organic compounds by biological agents like microorganisms. Biodegradation of petroleum hydrocarbons is a complex process that depends on the nature and the amount of the hydrocarbons present, while biodegradation is relatively noninvasive and more economical than other remediation technologies such as chemical and physical methods. As bioremediation is cost-effective and would lead to complete mineralization, it is the promising technology for the treatment of these contaminated sites. Bacteria are the most active agents in petroleum degradation, and they work as primary degraders of spilled oil in environment. Numerous scientific articles have covered various factors that influence the rate of oil biodegradation. Different factors influencing hydrocarbon degradation have been reported previously. In this study, two strains of Acinetobacter, A.sp 1 and A.sp 2, efficiently capable of degrading crude oil were isolated from North Shaanxi oil-contaminated soil. The influence of the salinity, pH, different N, P sources and inoculation amount on the degradation of crude oil was separately studied to obtain the optimum degradation conditions, and the performance of these two strains under the optimum conditions on crude oil degradation were further separately investigated by GC-MS(Gas Chromatography-Mass Spectrometer) method. The results showed that A.sp 1 was able to efficiently degrade crude oil under the salt concentration of 1%, pH 6-7, KH₂PO₄ and K₂HPO₄ as phosphorus source, urea as nitrogen source, an inoculum ratio of 4%, respectively, and in which a degradating rate of 60% can be reached under the combined optimum conditions. A.sp 2 was observed to efficiently degrade crude oil under the salt concentration of 1%, pH 7-9, KH₂PO₄ and K₂HPO₄ as phosphorus source, ammonium nitrate as nitrogen source, an inoculum ratio of 8%, respectively, and in which a degradating rate of 67% can be obtained under the combined optimum conditions. GC-MS analysis showed that A.sp 1 was performed efficiently for the hydrocarbon C₂₁-C₂₅ components of the crude oil. A.sp 2 was shown to efficiently degrade the hydrocarbon C₂₀-C₃₀ components of the crude oil. Microbial degradation is the major and ultimate natural mechanism by which one can cleanup the petroleum hydrocarbon pollutants from the environment. Our results may be helpful to establish an efficient biodegradation strategy for Hydrocarbon contamination.