Abstarct: In recent years, the use of gamma rays in various industries has greatly prospered. These include bone densitometry and medical imaging, explosives detection in the military industry, the evaluation of concrete strength in barriers, and numerous others. In 1939 natural gamma ray detection, which emits gamma radiation from radioactive elements such as uranium, thorium and potassium existing in the rock, was used in studies. Then in 1953, the gamma-gamma log was used to measure the gamma ray scattered from artificial sources. In this research, we investigate the possibility of discovering oil mines by using gamma rays densitometry. For this purpose, using different simulations of the laxyers of the earth and the oil mines, we analyze the quantities obtained to introduce a new method for discovering the oil mines whenever possible. In this study, simulations were performed using MCNP code. These simulations are performed for three different types of salty water, gas, and crude oils and are compared with the case where no material except sedimentary rocks is present. These simulations are carried out in five different stages, the results of which are expressed in order. We first simulated a portion of the Earth using the MCNP code to obtain the depth of penetration of the gamma rays for the five emitting sources from these simulations. In order to find the optimal location of the drilled wells for the quality of oil exploration using MCNP code, we have simulated a block consisting of sedimentary rocks with four holes which a detector is inserted inside each of these holes. The results of these simulations show that the optimum location is opposite the sources and the use of passing gamma is less error than the use of backscattered gamma. We then simulated a block with a hole inside using MCNP code to discover the oil mines, which three different types of simulations were applied. The first is related to the source without any disturbance, the second is to the disturbance caused by isotopes in nature and the third is to the source with disturbance caused by the isotopes in nature, which for elimination of the disturbance caused by the isotopes in nature, increased source activity has been applied to simulations. The results of these simulations indicate the possibility of discovering oil mines using gamma rays and the amount of activity needed to eliminate disturbance caused by isotopes in nature. Finally, simulations were performed using the Gamma Activation Analysis to discover oil mines, which yielded good results from those simulations to discover oil mines. The advantage of using this method is that since the minimum energy required to conduct 18.7 MeV carbon interaction is not necessary to investigate the isotopes in nature, since most of the energy emitted by them is less than 18.7, so the isotopes existing in nature do not cause any disturbance to these measurements.