The experimental study is aimed at investigating the effect of a high porosity stainless steel packing (solid fraction being equal to 0.5%) and the influence of alcohol (0.5% volume) addition on the hydrodynamics and the gas-liquid mass transfer characteristics of bubble column reactors. This particular packing is a stainless steel welded grid with a mesh size of 12.5 mm. Measurements were carried out in a 0.2 m diameter and 4.5 m height bubble column, operating with air-water and air-ethanol solution (0.5% volume) systems in co-current upflow. A perforated plate gas sparger was used. Using, several measuring techniques, systematic measurements of average gas hold up, local gas hold up, bubble size, liquid axial dispersion coefficients and volumetric mass transfer coefficients were performed. Experiments were carried out for several values of gas and liquid velocities with and without the packing. It is observed that the packing has a large effect on gas hold up, slip velocity, radial gas hold up profile, bubble diameter, liquid mixing and gas liquid mass transfer. Gas hold up and mass transfer characteristics of packed bubble columns are found to be superior to those of bubble columns and the axial dispersion coefficients are much lower. The results obtained also show that the alcohol addition leads to larger mass transfer characteristics. The effect of both the packing and the alcohol addition can be attributed to the delay in transition from homogenous to heterogeneous gas flow regime and thus enhancing the range of homogeneous gas flow regime. The packing can be introduced to control the hydrodynamics and mass transfer characteristics of bubble column. Moreover, it can be used to support a catalyst at high pressure and temperature. (C) 2004 Elsevier B.V. All rights reserved.