Studying sedimentary facies and diagenetic peculiarities are highly important for the understanding of carbonate- reservoir quality, including those of relatively poorly-known areas of great economic importance. The Early Miocene Rudeis Formation (~60–191m thick) is composed mainly of fractured/stylolitic, vuggy/moldic, bioclastic coralline/algal dolostone and biogenic limestone, with common occurrences of pore-filling anhydrite and pebble-sized anhydrite nodules. The diagenetic characteristics of the formation in the Zeit Bay Field (Gulf of Suez, Egypt) affect its reservoir quality, as can be deduced from the analysis of cores from six boreholes. Compaction, anhydritization, cementation and micritization decreased the reservoir quality, whereas dissolution, stylolitization and microfracturing enhanced the production potential.