One of the features of the South-East of South Australia, geologically referred to as the Gambier Embayment or Gambier Sunkland, is the occurrence of large quantities of clean carbon dioxide gas in subsurface reservoirs . These quantities are so large that one of these reservoirs is being utilised for the commercial production of carbon dioxide. Carbon dioxide is by no means a rare constituent within the earth crust. It is quite commonly associated with hydrocarbon gases as for instance in the natural gas of the Gidgealpa - Moomba region and it is formed invariably as a byproduct during the coalification of vegetable matter. However, the carbon dioxide encountered in the Gambier Embayment cannot be regarded as such a "common associated gas" and its origin may need to be explained in a different context.