The incorporation of air bubbles is one of the principal processes of bread dough mixing, providing the main route for oxygen adsorption into the dough and determining the bubble size distribution that will evolve into the final bread crumb structure. Pressure-vacuum mixing is the most sophisticated industrial technique for controlling these. This paper reports on a novel investigation into the mixing of bread doughs under controlled atmospheres of air and CO2. Industrial bread manufacturers apply a vacuum during the final period of dough mixing to enhance the break-up and disentrainment of bubbles, which results in a rapid reduction in the final dough gas content. A trial in a test bakery showed experimentally that a period of mixing under a CO2 atmosphere had a similar effect on the dough's final gas content as a period of vacuum mixing. The final loaves were inspected visually, were measured for volume (TexVol) and crumb structure (C-Cell). The C-Cell has proved to be a successful tool for measuring parameters which can be identified with the crumb changes in pressure-vacuum mixing. The enhancement in final loaf quality achieved by pressure-vacuum mixing was not fully reproduced by pressure-CO2 mixing, but the work established that pressure-CO2 mixing could be used to give control over aspects of crumb structure.