Asphaltene and wax depositions in the course of production of many Iranian reservoirs have become a serious problem. In order to investigate the effects of injecting rich and dry gases and also nitrogen, on the asphaltene precipitation process, a comprehensive research study was launched. The three phase equilibrium calculation of NGHIEM and his colleagues was used . In the method pure asphaltene in the oil was considered as solid and the heavy part of the oil was split as precipitating and non-precipitating. The provided model was able to describe the phase behavior of reservoir oil encountered with a compositional disturbance caused by injecting light fluids into the reservoir during the production period. In this work, first, the natural depletion model of each case was constructed and then the changes of behavior by injecting rich and dry natural gases and also high nitrogen content gas were investigated. Also the changes in the onset of asphaltene precipitation for different injections were shown. The achieved results showed that the nitrogen gas had more moderate effect on precipitation process compared to more vigorous effect of dry and rich gases.