Abstract: Based on the data of 54 giant gas fields discovered in the Persian Gulf Basin, this paper applies the concept and analytic method of petroleum system, dissects giant gas fields one by one, and probes into their formation and distribution in the Basin. Study shows that the source rocks of giant gas fields are Silurian Gahkum Formation, Qusaiba Shale Member, and Cretaceous Kazhdumi Formation. The reservoirs are mainly in Permian, Jurassic and Cretaceous strata. Giant gas fields are controlled by the tight limestone regional cap rocks in Lower Triassic Sudair Formation, the anhydrite seal in Upper Jurassic Tithonian Hith Formation, and the evaporite rock seal in Lower Miocene Fars Formation (Gachasaran Formation). The main trap is structural. In this region giant gas fields are mainly distributed in two regions: foreland area and passive continental margin, and gas is rich in different layers and formations in different regions. Gas distribution is mainly controlled by four factors: organic material type and gradation of thermal evolution of source rocks, accumulation conditions favorable for reservoirs, high-quality regional and local cap rocks, and structural elements like lateral compression, salt flow, and basement rift. They determine the distribution region and the accumulation zone of gas. It is predicted that there are three favorable exploration areas: the first is the “areas that have been explored and developed” and the exploration targets in these areas are structural; the second is the “areas that have been explored and developed” and the exploration targets here are nonstructural; the third is the “areas that have not been explored and developed”

Key words: giant gas field, petroleum system, formation, distribution, Persian Gulf Basin