Abstract: This article describes in detail some fundamental concepts of the Monte Carlo Method in estimating petroleum resource with the formula of the volumetric method. The computer program is also presented. The author made an estimate for petroleum resource of two oilfields with the Monte Carlo Method. Different models of probability of the main parameters, such as oil saturation, porosity and volume of oilbearing rocks, which would affect the estimate of petroleum resource were simulated. The results of petroleum resource estimation obtained in the simulations suggest that the estimate using statistical models of probability of a parameter is close to that obtained from the normal distribution model of probability derived from simulation, when sufficient original data of the parameter are available. Therefore, a parameter can be simulated with normal distribution model of probability when original data of the parameter are insufficient. In estimating petroleum resource, the Monte Carlo Method can be applied in combination with both the experiences of geologists and the actual geological data, no matter the geological data much or few. It can be considered as a practical method and widely applied in estimating oil and gas resources of various areas at different exploration stages.