This paper presents an experimental study of the countercurrent packed-bed column in the course of flooding and above the flooding point when the column operates as a packed bed and a bubble bed in series. Pressure-drop and liquid-holdup data are presented for the packed- and bubblebed parts of the system. The experiments show that for the two beds in series the hydrodynamic conditions within the packed-bed part are similar for various gas-liquid velocity conditions. The pressure drop in the initial stage of flooding is essentially independent of gas-liquid velocities. The porosity of the forming bubble bed is initially high/low for high/low liquid velocities, For expanded bubble beds their porosity increases with increasing gas velocities.