A theoretical analysis is presented of the effect of bubble coalescence on throughflow gas velocity. In order to predict the motion of interacting two-dimensional circular bubbles, bubble velocity is approximated by adding to its rise velocity in isolation the velocity that the particulate phase would have at the position of the nose if the other bubble were absent. It is inferred that throughflow gas velocity is significantly increased during bubble interaction as compared with the case of single isolated bubbles. Also, it was found that a lateral motion of the rear bubble is induced if the interaction bubbles are not vertically aligned.