The Lower Triassic Kangan Formation together with the underlying Upper Permian Dalan Formation forms one of the most important reservoirs for natural gas in the Middle East. The carbonate-dominated Kangan Formation was studied at a gasfield in the southern Persian Gulf and some 100 m of core were examined at micro- and macro scales. Twelve microfaaes were identified. Previous studies have divided the Kangan Formation reservoir into Lower (K2) and Upper (K1) Units. The Lower Kangan can divided into two subunits (K2b and K2a), while three subunits (K1c, K1b and K1a) are recognised in the Upper Kangan. Diagenetic processes have affected reservoir quality in the Kangan Formation in different ways. Processes improving reservoir quality include dissolution, dolomitization and fracturing, while reservoir quality was decreased by cementation, and chemical and mechanical compaction. Micritization and neomorphism have had both positive and negative effects. Fracture development has improved reservoir quality, particularly in dolomitic intervals.