Column flotation is an emerging technology in the deinking of recycled paper. Deinking efficiency depends primarily on the effect of four physical variables: gas and accepts flowrates, bubble size distribution, and pulp consistency. Experiments to establish operating ranges for these variables by determining their effect on gas holdup were conducted in a laboratory column installed at Bowater＇s Gatineau (Quebec) mill which processes a pulp (70% ONP/30% OMG) with about 1% consistency. The results showed the general trends expected From a review of previous studies: gas holdup increases with gas and accepts flow rates and with smaller bubble size, and decreases for higher pulp consistencies. However, the review also demonstrated that the published information is of limited application as the bubble size was much larger than that encountered in industrial flotation practice, primarily because of the use of pure water. Industrial pulps contain in most cases surface active agents which have a substantial effect on forming and preserving a small size bubble population.