The gas content of glass is an important factor which determines the glass quality concerning the number of bubbles and the fining behaviour. The determination of the amount of gas in glass, melted in industrial tanks is both an analytical and a sampling problem. Some difficulties are discussed concerning the determination of gas content in glass, melted in a tank, by means of modified equipment for evolved gas analysis. It could be shown that the variance of the gas content in a blob is strongly influenced by sampling procedure and not only by gas distribution in the melt.