Ensuring an adequate air-void system in concrete is essential to obtain proper resistance to freezing/thawing and deicer scaling. With increasing usage of highly flowable and self-consolidating concretes, it is important to ensure that these concretes can secure a proper air-void system that remains stable during agitation, placement, and setting. This paper gives information regarding the effect of mixture composition on the stability of an air-void system during agitation. Several mixtures made with various contents of cementitious materials and proportioned to ensure stability by different means were studied. The results will be of interest to engineers and concrete technologists involved in producing highly flowable, air-entrained concrete.