The solubility of a gas in a liquid increases with increasing gas pressure. When the external pressure is reduced, the excess gas comes out of solution.
Fizzy drinks are made by subjecting the liquid to carbon dioxide, under pressure. In champagne the CO is produced naturally in the final stage of fermentation. When the bottle or can is opened some gas is released in the form of bubbles.
Release of gas from supersaturated tissues can cause an underwater diver to suffer from decompression sickness (a.k.a. the bends) when returning to the surface. This can be fatal if the released gas obstructs critical blood supplies causing ischaemia in vital tissues.
Dissolved gases can be released during oil exploration when a strike is made. This occurs because the oil in oil-bearing rock is under considerable pressure from the over-lying rock, allowing the oil to be supersaturated with respect to dissolved gases.