Otoyol 51 (English: Motorway 51), abbreviated as O-51, aka Adana-Erdemli Otoyolu (English: Adana-Erdemli Motorway), is a tollmotorway in the Mediterranean Region of Turkey, connecting the cities Adana and Mersin. The motorway is on its full length of 88km (55mi) part of international routes as of European route E90 and Asian Highway 84.
The motorway starts from the west terminus of Adana Beltway O-50, runs westward reaching the south terminus of Pozantı-Adana Motorway O-21 northeast of Tarsus, continues southwest to Mersin bypassing it at north and terminates in Erdemli.