Abstract: The western region of China covers an area of 2.60 million km², where more than 100 oil/gas fields have been found and there are very abundant oil/gas resources. Through several decades of research and exploration, the petroleum-forming characteristics of compressional superimposed basins in the region have been summarized, including polycyclic evolution, seven properties of tectonic deformation, poly-epochal hydrocarbon source rocks, several reservoir rock-cap rock combinations, four phases of accumulation formation, distinctive characteristics of oil/gas accumulations and characteristics of petroleum distribution.