Based on the principles of petroleum accumulation system

this paper systematically summarizes and perfects the traditional techniques of petroleum resource assessment

and expounds the connotation of resource evaluation under a petroleum accumulation system. On the basis of a deep understanding of the controlling factors of petroleum accumulation and the principles of statistical models

we defined the key objectives of resource assessment at various exploration stages

categorized and standardized the most popular mainstream approaches used in the industry and academia

as well as methods evolved during the development of PetroV（ a petroleum resource evaluation system of Sinopec）

and proposed a methodology framework for resource assessment of a petroleum accumulation system. The categorized five methodology series include 1) probabilistic inference or analogue approaches for frontier targets

2) Monte Carlo approaches for conceptual plays

3) statistical methods for established plays in early exploration stage

4) probabilistic reasoning models for targets in mature plays and 5) discovery process and spatial statistical models in well explored regions. We elaborate the objectives of assessment and the suitability of statistical methods under a variety of exploration scenarios through real examples. In practice

the proposed assessment framework can effectively reduce the sensitivity on parameter selections and the impact due to differences in the geological models on output

thus enhancing applicability of the statistical methods. In addition

the proposed framework may also provide useful information for direction on future methodology development.