Abstract: Gas reservoirs of lower Permian (Yangxin Series ) are one of the major ones in south Sichuan Province. Such gas storage structures belong to fracture-karst cavern type. Based on the data obtained from gas exploration and development, karst phenomena of the lower Permian gas reservoirs may be classified according to their stage of formation and their burial depth into two different types: (1) paleokarst formed at the end of Dongwu epeirogenetic movement; and ( 2 ) deep karst formed after the Himalayan mov...