Abstract: Based on the latest exploration data, through study of basin evolution and analysis of hydrocarbon accumulation, the petroleum systems and hydrocarbon plays of the west Natuna Basin are identified, described and analyzed in this paper. The purpose of the endeavor is to assess the petroleum resources potential and geological risks so as to optimize the favorable exploration targets. The results suggest that the west Natuna Basin can be subdivided into 4 petroleum systems and 9 plays, of which 6 have exploration potential, and the undiscovered petroleum resources of the 6 plays are estimated as 890.16 MMboe in total by the Monte Carlo method and resource abundance analogy method. The undiscovered petroleum resources of the Penyu Formation play in the Penyu Sub-basin are up to 587.22 MMboe, accounting for 66% of the total of the basin. Upon the analysis of hydrocarbon accumulation factors using double factors method for resources-geological risks assessment, identified are plays including one class Ⅰ play, one class Ⅱ play, two classe Ⅲ plays and two class Ⅳ plays. Favorable exploration areas can be further optimized with the 'plays area overlaying' method. The stratigraphic-structural play in Arang Formation in the northwestern part of the Anambas Graben is finally selected as the most favorable area of class I. The progressive research method of resource assessment and division of hydrocarbon plays can guide the petroleum resources assessment in intracratonic rift basins of Southeast Asia.