Remediation of contaminated soil has been considered as an important environmental issue. Biological methods are widely acknowledged and used to alleviate the environmental problems associated with contaminated soil. Biodegradation involves a series of metabolic processes that decompose organic compounds into smaller and simpler subunits by the aid of microorganisms. Biodegradation has a great potential to treat soil and groundwater contaminated by a variety of hazardous chemicals such as

refractory organics, oils, benzene, styrene, vinyl chloride, pentachlorophenol, polyaromatic hydrocarbons (PAHs), toluene, xylene, phenols, etc. The present study focuses on the biodegradation of total petroleum hydrocarbons (TPH). The study was carried out to understand the effect of substrate concentration and type on the biodegradation rate and efficiency. Three sets of bioreactors were considered for the study, each set had 24 bioreactors. They were contaminated with different substrates i.e. diesel, lubricatingoil and waste oil at different concentrations to attain different initial hydrocarbon concentration. These bioreactors had no maintenance of any of the environmental parameters influencing bioremediation throughout the study period of 60 days. The performance and efficiency of the bio-treatment were evaluated for all the bioreactors. Maximum degradation was observed in lighter fraction of petroleum i.e. diesel and minimum degradation was observed in heavier fraction of petroleum i.e. waste oil, as lighter hydrocarbons evaporate in normal conditions.