The Quantitative high-resolution planktonic foraminiferal analysis of the subsurface section in three selected wells in the Ajeel Oil Field (Aj-8, Aj-12, and Aj-15) in Tikrit Governorate, Central Iraq has revealed that Shiranish Formation deposited in Late Campanian- Latest Maastrichtian age. This formation consists mainly of marly and marly limestone yielding diverse planktonic foraminiferal assemblages and calcareous benthic foraminifera, with a total of 46 species that belong to 23 genera, Three zones and four subzones, which cover the Late Campanian to the Latest Maastrichtian, were identified based on the recorded planktonic foraminifera and their ranges. They are as follows:1. Globotruncana aegyptiaca Zone that dated to be Late Campanian 2. Gansserina gansseri Zone that refers to Early Maastrichtian 3. Abathomphalus mayaroensis Zone that indicates Late Maastrichtian, in this section, the Abathomphalus mayaroensis Zone is divided into four subzones, namely in that order from bottom to top: Racemiguembelina fructicosa (Early Late Maastrichtian), Pseudoguembelina hariaensis (Middle-Late Maastrichtian), P. palpebra ( Late Late Maastrichtian), and Plummerita hantkeninoides (latest Maastrichtian).