Ostracoda from the Upper Cretaceous and Lower Tertiary iron five wells in Saudi Arabia have been examined. The Superfamily Cytheracea is studied in detail. It is represented by seventy-five species. Of these, seventy-one are new, one has been established by Siddiqui (1971),one by Al-Furaih (1975) and two are left under open nomenclature. Six new genera - Clinocythere, Hapsicytherura, Holcopocythere, Phyrocythere, Rhostocythere and Schizoptocythere - and two new subgenera - Otarocythere and Prophalcocythere - are described. A modification of the Liebau diagram for the analysis of the ornament has been adopted. The Upper Cretaceous and Lower Tertiary formations from two wells (Abgaiq W-69 and El-Alat W-1) are divided into five ostracod biozones and a correlation with the previously established foraminiferal zonal scheme for the Umm er Radhuma Formation is discussed. All the evidence indicates that the Aruma and Umm er Radhuma Formations were deposited in a shallow water, mainly carbonate, environment.