Through modern technology we can use the void pore space of underground rock formations for a growing number of socially beneficial purposes. These run the gamut from unconventional oil and gas production to climate change mitigation. The common law of property and tort, however, has struggled to keep up with advancing technology in this area. Significant questions remain about the nature of property rights in pore space. Of particular interest are the limits, if any, on an owner’s right to use pore space for beneficial purposes when it extends beneath the land of another. For example, may A hydraulically fracture an oil well on her property if the fractures extend beneath B’s land? May C store anthropogenic carbon dioxide for climate change mitigation in a common reservoir that extends beneath the land of D, E, F, and G if they do not consent? If so, what, if any, compensation does C owe to the others? These and similar scenarios pose urgent questions for a wide range of landowners, industries, environmental interests, courts, and policymakers across the nation.

This Article searches for answers to these pressing questions in the doctrinal histories of similar common pool natural resources. The Article reviews the development of common law rights in water and oil and gas to synthesize lessons for shaping the content and limits of rights in pore space. Then, applying these lessons to the current state of pore space rights, the Article explains that rights in pore space are established by a default rule of prior use and are absolute, subject to little, if any, limitation. As demand for the resource continues to grow, however, owners, and, ultimately, courts will likely search for ways to limit the absolute extent of pore space rights to avoid a tragedy of the pore space commons.

In searching for doctrinal mechanisms to make pore space rights limited, or correlative, the Article predicts that courts will be tempted to choose between establishing limits by strict, formalist rules of proportionality (which favor certainty), on the one hand, and instrumentalist, utilitarian standards of reasonable use (which favor development of the resource), on the other. This Article identifies an underexplored doctrine from oil and gas law that would define the limits of pore space rights without resort to purely instrumentalist or formalist doctrines. The “fair-opportunity doctrine” articulated here would permit an owner to use any quantity of pore space anywhere in a common reservoir, so long as it does not interfere with the lawful existing operations of other owners or deprive other owners of a fair opportunity to either participate in the proposed operations or conduct like operations from their respective land.