On use of simple model aqueous sodium bicarbonate solutions and Celgard 2400 gas permeable membranes, bicarbonate disproportionates to carbon dioxide and carbonate when gaseous carbon dioxide is removed from the water by diffusion through gas permeable membranes at elevated water pressures. The permeability of CO2 by phase transition from bicarbonate solutions at pressures of 500 psi is only possible because of the use of multiple gas permeable membrane layers. The multiple layers minimize water permeability at pressures near or above the Young-Laplace bubble point of single membrane layers, and the gas permeability efficiency and rate are greatly decreased.