Tulsa is the second-largest city in the state of Oklahoma and 46th-largest city in the United States. It is the principal municipality of the Tulsa Metropolitan Area. Tulsa’s CSA is projected to reach one million. The city serves as the county seat of Tulsa County, the most densely populated county in Oklahoma, and extends into Osage, Rogers, and Wagoner counties. Once heavily dependent on the oil industry, economic downturn and subsequent diversification efforts created an economic base in the energy, finance, aviation, telecommunications and technology sectors. The Tulsa Port of Catoosa, at the head of the McClellan-Kerr Arkansas River Navigation System, is the most inland river port in the U.S. with access to international waterways. Two institutions of higher education within the city operate at the NCAA Division I level, Oral Roberts University and the University of Tulsa.