The diffusion of CO2 through macroand micro-agglomerated cork stoppers for sparkling wine was studied by a manometric technique. The effective diffusion coefficients for each part of the stopper (cork body, cork disc and adhesives) were determined for the first time. The results show that a small particle size along with a high adhesive content and level of compression favor the gas barrier properties of the cork stopper. Although the cork discs placed at one end of the stopper present no resistance to gas transfer, the adhesive film between them constitutes a high barrier to gas transfer. The mechanism that controls the gas transfer is the solution-diffusion process through the polymeric chains of the adhesive. Although the aging of the cork stopper and the gas transfer at the glass/stopper interface were not considered, results clearly showed that the cork stoppers studied were capable of maintaining a CO2 concentration in the bottle that is sufficient for conserving a good effervescence of sparkling wines over several years.