Geological storage involves injecting CO₂ into rock formations deep underground, thereby permanently removing it from the atmosphere. It may also be referred to as geological sequestration. Geological storage or sequestration may be viewed as means of recycling excess carbon back into the geosphere, where it came from in the form of fossil fuels. CO₂ and the minerals it forms - such as calcite - are naturally occurring and widespread in the subsurface.

Sandstone rock formations are a typical target for geological storage of CO₂. They are slightly porous and permeable, even at a depth of one kilometer or more below the surface. Fluids within the sandstone are isolated from the atmosphere and underground sources of drinking water by many hundreds of meters of impermeable bedrock.