Abstract: A gas sampling method and apparatus for determining the volume of air present in carbonated liquid in bottles and cans and in process lines. The method comprises testing a predetermined quantity of liquid containing CO.sub.2 gas by absorbing free CO.sub.2 gas evolved from said liquid in a liquid CO.sub.2 -absorbent solution whereby any air is concentrated as a residual gas and subjecting said liquid CO.sub.2 -absorbent solution with residual gas in a confined volume under a predetermined compressive force and measuring any resulting volumetric change whereby the volume of air present can be determined.