To add to others, awesome (from a returns perspective) tax structures like MLPs mean that energy infrastructure is heavily subsidized because income generated through MLPs is either not taxed at all or taxed at a very advantageous rate compared to traditional corporations. The government in the US has set these up primarily to incentivize investment in energy infrastructure and real estate. Energy Transfer Partners - the company most recently known for trying to build the Dakota Access Pipeline - is one such MLP.