Abstract: Reservoirs of Sarvak Formation in the Y Oilfield of the Zagros Basin,Iran are rich rudist-bearing chalky limestone.Reservoir spaces are mainly porosities and vuggs,with few fractures.The reservoirs were deposited in slope of marginal neritic carbonate platform and marginal reefs.The heterogeneity in intralayer is weak while strong in interlayer.In charge of sedimentary environment and diagenesis,high-quality reservoirs developed in slope of marginal neritic carbonate platform and marginal reefs which with slightly chalk-diagenesis.Sarvak Formation is a multi-layer stacked reservoir with weak edge water and a tilted oil-water contact.Development must depend on reservoir characteristics and reservoir types.