A Pennsylvania appellate judge on Monday distinguished [opinion, PDF] the natural gas extraction practice known as hydraulic fracturing, or “fracking,” from conventional drilling property rights and held that fracking is not subject to the same “rules of capture.”

In a suit brought against Marcellus Shale gas producer Southwestern Energy [corporate website] alleging trespass and conversion for producing gas under the plaintiffs’ land, Senior Judge John Musmanno of the Superior Court of Pennsylvania [official website] explained that Pennsylvania courts have yet to determine whether the processes unique to fracking prevent its application to the same law of capture as traditional methods of drilling.

Traditionally, the rules of capture assume that oil and gas originate in subsurface reservoirs or pools, and can therefore migrate freely within the reservoir and across property lines. However, the court explained, this is not true for the oil extracted via fracking from the Marcellus Shale formation.

“Shale gas does not merely ‘escape’ to adjoining land absent the application of an external force,” the court said.

The court concluded that the rule of capture does not prevent liability for trespass due to fracking. The court did not rule on whether Southwestern actually trespassed on the property, but rather sent the case back to the Susquehanna County Court of Common Pleas to determine the facts in light of the Superior Court’s ruling.