When it comes to industries with major barriers to entry, one market looks especially interesting: natural gas pipelines. Environmental and zoning restrictions make building new pipelines a practical impossibility. Meanwhile, gas usage seems almost certain to rise over the long term. Greater use of gas now depends on the capacity of pipelines to move it from the fields where it’s produced to additional places where it could be used effectively, so the companies that already have a dominant position will continue to enjoy a partial monopoly in their service areas. NiSource (NI), a utility based in Indiana, owns Columbia Gas Transmission, one of the largest pipeline networks in the U.S. Columbia transports massive amounts of natural gas to the Northeastern and Midwestern U.S. The shares trade at less than 14 times estimated earnings for the coming year and pay a 4.5% annual yield. Spectra Energy (SE) in Houston owns Texas Eastern transmission and brings gas to large swaths of the U.S. The shares trade at less than 14 times estimated earnings for the coming year and pay a 4.1% yield.