Abstract: Pareto presented a negative exponent power function in 1897 to describe the distributions of reserves scale of oil and gas fields in petroliferous regions or basins, which is called Pareto distribution model or Pareto law. However, the original Pareto distribution model has some flaws in theory—N(0) approaches to infinite when x equals to zero. Furthermore, the constants in the distribution model can’t be determined because there is usually a nonlinear relationship between reserves scale and its serial number on double-logarithm coordinate. Therefore, Pareto distribution model can’t be applied effectively in oil and gas resources evaluation. Chen Yuanqian presented a modification of the original Pareto distribution model in 2008 to overcome the theoretical flaws and established effective estimation methods. Then the methods to calculate Pareto distribution density, cumulative distribution and adverse cumulative distribution, total resources and 3-level resources are obtained based on the modified Pareto distribution model. At the same time, this paper reviews the 3 incorrect Pareto distributions presented by Jin Zhijun, Lee and Chen-Richard, respectively. The actual application indicates that the new methods are practical and effective