The influence of pressure on the gas hold-up in a bubble column is determined for a sodium sulphite solution in combination with the volumetric mass transfer coefficient. Furthermore, for the same conditions the bubble size is also estimated from photos. The results of these experiments show that the interfacial area and the volumetric mass transfer coefficient both increase with pressure, while for design purposes the magnitude of the increase can be safely estimated from the increase in gas hold-up. Finally, the influence of pressure on the Sauter mean bubble size in a number of pure liquids (mono-ethylene glycol, n-heptane and deionized water) is also studied and correlated with a new empirical equation on the basis of photos in combination with literature results.