Most oil refineries in the United States are located nearby port areas as coastal cities are large consumption markets. Since the 1960s, domestic oil production has been declining, and oil imports have been increasing, which reinforced the locational relevance of coastal refineries. As such, the length of domestic oil pipelines did not change much, even as national consumption increased. Since 2005, strong growth in domestic shale gas production has placed pressure on the development of additional gas pipelines. This expansion has led to a substantial increase in the length of gas pipelines with the reconversion of existing oil pipelines, adding additional pipelines along an existing line, and expanding the network to service new areas and markets. Such developments match the ongoing transition of global energy systems from liquid energy sources, such as petroleum, to gas energy sources, such as natural gas.