The pressure balancing act in geological storage: sharing the subsurface for the common good

Large-scale geological CO₂ storage (GCS) is essential for achieving net zero targets: its scalability is constrained less by pore volume occupancy than by pressure space—the finite capacity of connected formations to dissipate pressure increases without causing undesirable consequences (such as brine expulsion, induced seismicity, and lower injection rates for a given surface pressure). Current regulatory and commercial frameworks focus on project/site scale containment of CO 2 , but as multiple projects start to inject in the same storage formation, the cumulative pressure buildup will limit injectivity long before pore space is filled with CO 2 . Here we synthesize the physics of pressure propagation, the geomechanical limits, and interference across multiuser aquifers, and review monitoring and modelling strategies from analytical screening to full field simulations. Drawing on analogues from groundwater management and three regional illustrative examples (Horda Platform, Paris Basin, Captain Fairway), we show that pressure footprints can exceed plume extents by two orders of magnitude and propagate across tens to hundreds of kilometers. We argue that commons-based governance, underpinned by effective monitoring, open data, regional models, and adaptive allocation of pressure budgets, is essential for safe, efficient, and equitable storage. Treating pressure as a shared resource is not optional: it is the foundation for gigatonne scale CO₂ storage and sustainable multiuser use of the subsurface.