This chapter studies doctrines that consolidate different real-world resources into different res in property law. Some such doctrines classify individual real-world resources as separate res; others consolidate several resources into single res in law. The requirements for natural property rights, namely, claim communication and productive use, provide satisfying foundations for thing design doctrines. The doctrines are then implemented in law and policy via practical reason. This chapter studies doctrines associated with accession, specification, confusion, fugitive or fugacious minerals, the ad coelum maxim, the ratione soli maxim, and fixtures. This chapter also studies how property in land, water flow, and chattels all limit one another. This chapter also studies contemporary policy debates about hydraulic fracturing, including property in oil and natural gas trapped in shale or “tight” rocks.

The suggested shift in policy perspective from groundwater to aquifers challenges the traditional approach to groundwater as a public resource issue. The legal issues involving aquifers are a complex combination of public rights and private property. Groundwater is traditionally a publicly held resource, yet the aquifer’s storage space appears to be considered private property. Although these resources are interconnected, courts have taken different approaches to addressing conflicts that involve indirect effects of groundwater extraction, like subsidence and subterranean trespass. Some states and courts treat pore spaces akin to a mineral right and protect private uses, like carbon sequestration. In other cases, courts have treated pore spaces as a public resource and refused claims of trespass and nuisance when adjacent aquifer uses interfered with private property rights. There is no clear consensus as to the ownership of aquifer pore spaces.