Abstarct: Nowadays, soil contamination due to hydrocarbon oils is considered as an important environmental issue in the world and there are many concerns about the groundwater pollution with these toxic substances. Therefore, the transport and diffusion process of these substances in the sub-surface have been considered. The leakage of light and dense hydrocarbon contaminants, passing through the unsaturated zone and reaching groundwater aquifers, is one of these concerns. In this research, the factors affecting the spread and release of oil pollution in unsaturated soils and groundwater have been investigated. Using a numerical model in order to simulate the release of pollutants in porous media is the purpose of this study. The CTRAN/W software which is baxsed on finite element, was used to model the movement of pollutants in the soil. Generally, the effects of various factors such as permeability of the soil, inflow discharge of contaminant, density, etc. in a porous and semi-saturated area of 50 meters in length and 30 meters in depth, which has a water table and the source of contaminant is In the middle of that, has been investigated. The results indicates that there is a vertical propagation pattern in the coarse soils and a horizontal pattern in the fine soils.