Biodegradability of hydrocarbons on soils can be applied to the treatment of residues (land treatment) from petroleum refinery as well as the cleaning of contaminated soils (bioremediation). In this paper we have studied the biodegradability of hydrocarbons from petroleum tank bottom sludges on soil by the autochthonous microbial community. Lab assays were conducted in 1l-beakers under the following conditions: hydrocarbon load 5.3%, total aerobic microorganisms 2.7 x 10(7) CFU/g, hydrocarbon degrading microorganisms (HDM) 2.5 x 10(5) cells/g, incubation temperature 25 degrees C, pH 7.0-7.6, and moisture 10-15%. Soil had the following composition: sand 25%, silt 15%, and clay 20%. Different levels and kind of fertilizers were evaluated. Fertilization increased the rate and the quantity of hydrocarbons degraded. It was degraded about 40% of hydrocarbons in 30-90 days according to the fertilization effected. During biodegradation, the HDM increased 760 times. Assays conducted outdoor on trays showed a similar limit of biodegradation. Changes with time in the fungi population, hydrocarbon class, carbon level, and saturated hydrocarbon profiles were measured too. Data suggests the use of microorganisms having a greater metabolic capacity, specially to degrade those hydrocarbon classes that they have shown to be more resistant to biodegradation (aromatics, resins and asphaltenes).