A pipeline is a tubular conduit that transports liquids, gases or suspended solids from one place to another. Depending on their size and contents, pipelines may rely on pumps, valves and other devices to manage their flow. Although many pipelines are buried out of sight, they can also be found aboveground and underwater.
Pipelines carry a wide range of substances, but fuels such as oil and natural gas are among their most common — and controversial — cargo. While pipelines often move fuels more efficiently than other methods, they can also endanger nearby people and wildlife. Several recent U.S. accidents have highlighted this risk, including a 2010 explosion in California, a 2010 spill in Michigan and a 2013 spill in Arkansas. The potential for spills is also a factor in debates about the proposed Keystone XL oil pipeline, which would stretch 1,100 miles from Canada to Texas.
Oil and gas pipelines cover more than 2.5 million miles in the U.S. alone, with a yearly average of 281 "significant incidents," 18 fatalities, 73 injuries and $320,000 in property damage, according to data from the federal Pipeline and Hazardous Materials Safety Administration. Regular maintenance and repairs can help reduce the likelihood of such accidents. (Photo: Shutterstock)