Area code 539 is an overlay for area code 918 in northeastern Oklahoma, serving cities such as Tulsa, Broken Arrow, Muskogee, and Bartlesville. It was introduced in 2011 to meet the growing demand for phone numbers in one of the state’s most populous regions. Ten-digit dialing became mandatory across the 918/539 territory. Tulsa, the second-largest city in Oklahoma, anchors the region with its energy sector, arts scene, and historical significance as a former oil capital. While 918 is the legacy code, 539 is now widely used for newer lines. It supports a dynamic and expanding metro area in eastern Oklahoma.