The purpose of this study is to discuss the general geology of the Adana Basin and especially to make a detailed description of the Lower Miocene formations, situated to the northwest of the Mersin - Tarsus region, and to review in a general way the oil possibilities of the basin, with a particular stress on the importance of the Lower Miocene formations in this connection.The Adana Basin is divided into three regions : The Hatay ( = Antakya), İskenderun, and Adana regions; the latter is subdivided in its turn into two secondary regions, namely the Adana and Mersin ( = İçel) regions. The direction of the tectonic ridges dividing these regions is NE-SW. The general features of sedimentation in these regions are more or less alike; however, some differences have been observed. Although transgressions are predominant in the Miocene, regressive movements have also taken place. At places, the Lower Miocene overlies discordantly the Paleozoic, Mesozoic, Paleocene, Lutetian and Oligocene formations. The Lower Miocene consists of conglomerates, limestones, sandy limestones, marly limestones, and marls; lateral and vertical facies changes can be observed here. The calcareous parts are, in some places, reef-complex or biohermal in character. The reefs are transgressive and they more or less follow the direction of the buried ridges and hills, which are older in age. Despite the fact that the Lower Miocene is more calcareous at the periphery of the basin, towards the center, it turns into fine-grained sediments. In the middle of the basin shales are predominant. The thickness of the Lower Miocene calcareous formations in the Adana Basin is 80 m. near Kozan and some 500-700 m. in the proximity of Mersin. It may be said that in the vicinity of Misis it is practically missing. It is most probable that the Alpine tectonic forces came from the NW and the SE, the direction of folds is NE-SW on the western and northwestern borders of the basin, and partly E-W in the center. These folds are monoclinal. The southern parts of many of the anticlines have steeper slopes. In general, the Miocene presents folds with slopes gradually decreasing towards the upper layers. Certain structures are in the form of terraces. Faulting in the Tertiary is rare. The folding and faulting movements in the İçel section of the Adana region, as compared with other regions, have been more frequent, violent, and irregular.