|Abstract||Pollution, due to activities related to the oil industry, represents a serious threat to the natural environment. The application of biotechnological methods provides much safer and sustainable alternatives for bioremediation of polluted areas, using microorganisms. Several techniques for the isolation of hydrocarbon degrading bacteria have been investigated and published worldwide. A wide range of bilogical activities was shown. However, local hydrocarbon degrading strains and the factors affecting bacterial and strains variability were not studied deeply. In this study, we showed that the isolation and screening strategy affected a lot, the selection of the strains. We combined the bacterial tolerance to hydrocarbon toxicity, assessed by the growth parameters, and the bacterial degradative activities, assessed by the degradation of a wide range of petroleum hydrocarbons via Gas Chromatography analysis. The main investigations and findings of the present work are: -A collection of 39 bacterial isolates from the Qatari environment was set up and a new isolation and screening program was proposed. -The Growth conditions and the activity of pre-selected strains -Shift of the activity of the selected strains from a range of hydrocarbons to another by the effect of the nitrogen source, C/N ratio and organic nitrogen source -70% hydrocarbon removal, achieved with several strains in 2 weeks. -Amongst 12 identified isolates and by molecular ribotyping-DNA sequencing, 3 Pseudomonas strains isolated from a polluted area in Qatar, are available for bioremediation of highly polluted soils, tolerating high toxicity and may be adapted to a variety of low or high molecular weight hydrocarbons.