Contaminated sites are areas where, due to accidental spills or illegal deposits, polluting substances are present in the soil and are dangerous for humans and the environment. These are hydrocarbon contaminants, in particular the compounds making diesel. We know many engineering techniques for remedying it; some of them have been developed in recent decades, called bioremediation. They exploit the degradation of contaminants by microorganisms, for a lower impact on the ecosystem and considerable economic savings. Microorganisms are suitable for diesel degradation, capable of degrading a good percentage of contaminant. In contaminated microcosms we have a much higher CO2 production than biotic controls (uncontaminated microcosms), with a progressive mineralization of diesel, data confirmed by gas chromatograph analyzes. Reductions of order of 70% for diesel are also obtained. By in-depth analyzes on the gas chromatograph, it can be highlighted that low molecular weight compounds are degraded in percentages greater than 90%, while high molecular weight compounds are reduced by 35-40%. Microbial populations are therefore able to use pollutants as a source of carbon and energy. There is still a limited knowledge about processes and microorganisms involved in the degradation of hydrocarbons in marine environment. Then it is of primary importance to deepen the phylogenetic and functional diversity of microbial communities, virtually involved in the biodegradation of hydrocarbons. Highly contaminated sites are unexplored sources of microorganisms with high potential for studying bioremediation processes and for the growth of new strategies in the field of environmental remediation.