Sinjar Mountain is an outstanding structural and geomorphic feature in the northwestern part of Iraq. It forms a long anticline in which the oldest exposed rocks belong to Cretaceous age represented by Shiranish Formation. The exposed succession includes rocks of many formations, which range from Cretaceous to Late Miocene. The presence of Oligocene rocks, however, has been a matter of debate. The main aim of this study is to prove the presence or otherwise of the Oligocene formations in Sinjar anticline. To achieve that, the planktonic foraminifera of an exposed section, starting from the top of Jaddala Formation (Eocene), were utilized to interpret the biostratigraphy, and zonation of the sections. The planktonic foraminiferal assemblages of the section were found to represent the Early Miocene (Aquitanian – Early Burdigalian) of Globigerinoides quadrilobatus primordius-Paragloborotalia kugleri Zone (N.4), Globoquadrina dihescens praedehiscens-Globoquadrina dehiscens dehiscens Zone (N.5), and Catapsydrex stainforthia-Catapsydrex disimilis Zone (N.6). Sparse fauna representing the Globigerina angulisaturalias-Paragloborotalia opima opima Zone (N.2) of Late Oligocene age, representing Ibrahim Formation, which is unconformably overlain by the Serikagni Formation. The Jeribe Formation of early Middle Miocene age of Globorotalia barisanensis Zone (N.9) overlies the Serikagni Formation; the contact is also marked by a major erosional unconformity. The regional geology, including data from the drilled oil wells in the nearby areas, was also reviewed, in order to delineate the extension of surface and subsurface basin of the Oligocene rocks. Moreover, many recently published articles that suggest the presence of Oligocene formations in Sinjar anticline were argued and it was found that the exposed studied sections belong mainly to the Early Miocene Serikagni Formations, with presence of a few centimeters of Oligocene rocks only.