The long-term accumulation of a substance; such as, carbon dioxide or radioactive waste, in a natural geologic formation, for example a sedimentary basin, seabed, or underground cavern: Jack and the geologists were exploring the possibilities of having a geological sequestration in the mountains.

A major demonstration of carbon dioxide injection into a saline formation for sequestration is underway at an offshore gas platform in the North Sea near Norway. Results from this project (and others) suggest that such formations will be reliable for long-term geologic sequestration (storage) sites or carbon dioxide reservoirs.

There are numerous natural carbon dioxide reservoirs throughout the Rocky Mountain states of the United States in geologic "domes" and "traps" suggesting these geological storage formations will be excellent for keeping carbon dioxide captured from industrial facilities.