A wide range of organic chemicals enter into the environment intentionally or unintentionally, creating public concern. Petroleum hydrocarbons are one of these organic pollutants with various hazards to terrestrial and marine ecosystems. We need cost effective technologies for restoration of contaminated sites. Bioremediation is one the methods which has been used in recent decades. In this method microrganisms and plants are used to remove degrade or stabilize pollutants. In the current study, oil degrading bacteria were investigated in petroleum contaminated soils of five oil refineres (Tehran, Shiraz, Isfahan, Abadan, Tabriz). Soil samples were collected and some physical and chemical characteristics including organic carbon, microbial respiration, percentage of lime, concentrations of petroleum hydrocarbons and heavy metals were measured. Oil degrading bacteria were isolated and purified after enrichment stage. 12 strains with the highest growth in a medium containing crude oil were selected for identification. DNA was extracted from the selected strains and a fragment of 16SrRNA gene was sequenced. Genetic diversity of the obtained sequences were investigated and phylogenetic trees were constructed using software MEGA v.4. Identified bacteria belonged to 5 species: Achromobacter spanius , Klebsiella quasipneumoniae , Ochrobactrum intermedium , Citrobacter amalonaticus , Pseudomonas aeruginosa . Growth and decomposition ability of these bacteria in media containing light and heavy diesel and crude oil were examined. Bacteria with the greatest growth and decomposition ability of crud oil, light and heavy diesel were Citrobacter amalonaticus , Klebsiella quasipneumoniae in and Ochrobactrum intermedium , respectively. Two A and B consortiums of bacteria were prepared. Consortium A was made of all five bacteria which showed the greatest growth in heavy diesel. Consortium B consisted of three bacteria ( Citrobacter amalonaticus , Klebsiella quasipneumoniae in and Ochrobactrum intermedium ) with the highest growth in crude oil. Thus, consortium A, B, could be used for decomposiion of heavy diesel and crude oil, respectively.The species diversity was evaluated, which showed a high diversity of oil degrading bacteria in the selected sites. Based on the results, it is recomended to investigate the ability of the identified bacteria in petroleum contaminated terrestrial and aquatic environments. Keywords: Soil, Petroleum hydrocarbons, Bacteria, Bioremediation, Genetic diversity, 16S rRNA gene