This work presents an analytical and interpretative perspective on the results of a study carried out by theauthor in Brazil with three classes of bacteria generally involved in the processes of soil biodegradation (sulfate reducingbacteria, nitrate reducing bacteria and iron reducing bacteria )). The objective of this work was to show the importanceof studies of biodegradation of monoaromatic hydrocarbons in soils with native soil bacteria. Benzene, toluene,ethylbenzene and xylenes, known as BTEX are commonly found in locations near oil refineries and by-products, fillingstations, or around pipelines from leaks and / or spills. The study found evidence that BTEX compounds can be removedunder anaerobic conditions in the presence of nitrate and sulfate. The results also show the importance of performinga preliminary characterization of the microbiota present in the environment before starting a bioremediation process.