Tenaska is a private independent energy company based in the United States. The employee-owned company was founded in 1987 and headquartered in Omaha, Nebraska, with regional offices in Dallas, Denver, Pittsburgh, Philadelphia, Boston and Calgary, and Vancouver, Canada. Tenaska and its affiliates develop, own and operate non-utility power plants; market natural gas and electric power; provide energy risk management services; and are involved in asset acquisition and management, natural gas exploration, production and associated transportation systems, and electric transmission development. Tenaska is recognized annually for operating safe, efficient, reliable power plants. The Natural Resources Defense Council (NRDC), an environmental organization, has listed Tenaska in benchmarking studies since 2004 as having among the lowest fleet-wide average emission rates for fossil-fueled power plants in the United States. The 2015 Top 100 Green Utilities report, published by trade journal Energy Intelligence, lists Tenaska 44th among power generators worldwide, based on low greenhouse gas emissions and the size of its renewable energy portfolio.