Seismic reflection work was carried out in the southwest of Ankara around Polatlı-Haymana region as part of "Haymana Oil Exploration Project" The project area is located in Polatlı Basin extending in NW-SE direction and covering Triassic to Quaternary sediments. Seismic reflection data were recorded along profiles of 426 kilometers located in the area by Ünalan's work (Ünalan et al., 1979) in which the stratigraphy of the Upper Cretaceous-Lower Tertiary are described in detail. The upper boundary of Beyobası formation is the best reflector level in the data. This Maestrichtian Formation has been considered as the reservoir formation because of its fossileferous sandstone and limestone content. The contour map of the Beyobası formation was prepared and interpreted. The transition bands in the stratigraphic layers are generally not identified sufficiently. As the result of interpretation a NW-SE directional fault zone and two highs at both sides of this zone in the east part of the project area were obtained. The highs in the north and south of this zone are considered as parts of Kızılcakışla and Eski Polatlı anticlines. However, the north closing of the high located in the north and the south closing of the high located in the south could not be seen in the seismic data. In the west part of the project area two synclines were observed. The closing of one which is placed in the south is observable and the closing of the other one located in the north is not clearly observable.