Last week, Pennsylvania Supreme Court settled a Marcellus natural gas rights dispute that's been in lower courts since 2011.
In Butler v Powers, the court justices took up the issue of whether or not natural gas rights should be part of the broader concept of "mineral rights" in PA. In most states when a deed or lease agreement is signed for mineral rights it includes natural gas as well, on the theory that the gas comes from a mineral—shale rock. But that has not been the case in PA. Going all the way back to a case in 1882, PA has had "the Dunham rule" which separates natural gas rights from the broader concept of mineral rights.
In brief, that rule says natural gas, for the purposes of deeds, contracts and leases, is not a mineral right. If you want to sell or convey the rights to natural gas under your property in PA, you have to specifically state "natural gas" in a deed, lease or contract. One family (the Butlers) sued the heirs of another family (the Powers) claiming the gas under their property was all theirs. In 1881 (one year before the Dunham rule) the Butler forebear deeded half of the mineral rights under the property to the forebear of the Powers family. Powers' descendants are now claiming natural gas as part of the original deal. But the Butlers maintain because "natural gas" was not specifically mentioned, the gas rights were not part of the deal, according to the Dunham rule.
A Susquehanna County court agreed with the Butlers. It's plain by any reading of the law: the Butlers are correct—natural gas rights were not conveyed if you use the standard set up by the Dunham rule. But on appeal, the PA Superior Court disagreed with the lower court saying the case should be reconsidered apart from the Dunham rule—in essence challenging the Dunham rule itself. Most other states consider natural gas to be part and parcel of "mineral rights" and PA Superior Court thinks its high time PA do the same (see this MDN story for more background).
A case filed several years ago in Susquehanna County, PA sought to overturn the Dunham rule and join gas and mineral rights back together, which would have been disastrous for thousands of lease and royalty agreements already in place. Dissolving the Dunham rule would have "changed the rules of the game" long after the game had started and likely would have thrown the drilling industry in PA into chaos–stopping drilling activity until agreements could be renegotiated and/or litigated. A real mess.