Since many of the wells found around the world contain heavy crude, this process increases their production.
Recycling of natural gas or other inert gases causes the pressure to rise in the well, thus causing more gas molecules to dissolve in the oil lowering its viscosity and thereby increasing the well's output.
Air is not suitable for repressuring wells because it tends to cause deterioration of the oil, thus carbon dioxide or natural gas is used to repressure the well.
This has been proposed as a method to combat climate change, allowing mass storage of CO2 over a geological timescale.
Reinjection of carbon dioxide in the Norwegian Sleipner gas field saves the operators 1 million Norwegian Kroners per day in national carbon taxes.