TC PipeLines, LP is a limited partnership company that acquires, owns and participates in the management of energy infrastructure businesses in North America. The Company's pipeline systems transport natural gas in the United States. The Company has approximately four pipelines and equity ownership interests in over three natural gas interstate pipeline systems that are collectively designed to transport natural gas from producing regions and import facilities to market hubs, and consuming markets primarily in the Western, Midwestern and Eastern United States. All of its pipeline systems are operated by subsidiaries of TransCanada. Its pipeline systems include Gas Transmission Northwest LLC (GTN), Northern Border Pipeline Company (Northern Border), Bison Pipeline LLC (Bison), Great Lakes Gas Transmission Limited Partnership (Great Lakes), North Baja Pipeline, LLC (North Baja), Tuscarora Gas Transmission Company (Tuscarora) and Portland Natural Gas Transmission System (PNGTS).