Area codes 918 and 539 are telephone area codes serving northeast Oklahoma. These area codes cover the following major cities: Bartlesville, Broken Arrow, Gore, Jenks, McAlester, Muskogee, Okmulgee, Sapulpa, Tahlequah, Tulsa, and northeastern Oklahoma. Area code 918 was created in 1953 as a split from area code 405. Area code 539 was created as an overlay for 918. It became active on April 1, 2011 (although 539 numbers could have been assigned for activation before that date). Mandatory dialing of ten-digit area codes became active on March 5, 2011. It is the first overlay in Oklahoma.