Performance studies on sieve trays with 1 inch diameter perforations are reported. Few published studies exist on such large hole sizes as compared with other sizes such as 3/8 and 3/16 inch diameter holes. Two columns, one rectangular (3 ft X 1 ft ) and the other round (32 inch diameter) were examined in a large pilot rig. The hydrodynamics of the columns have been investigated with respect to tray pressure drops, aeration and froth properties, and entrainment of liquid by vapour on the trays. Dry tray pressure drop studies have been used extensively to examine the validity of some of the commonly employed published correlations and to determine their applicability to large hole sizes. An extensive study of entrainment has been carried out to evaluate the effects of tray spacing and operating variables. The results have been successfully correlated by equations previously established by Kister et al. This is important as no results appear to be available for such large hole sizes. The mass transfer efficiency of the absorption system, air-CO2-water has been reported with a critical examination of sampling technique and method of analysis. These are shown to critically affect the evaluation of solute concentration in solution. The degree of liquid mixing has been investigated by a tracer injection technique. Liquid residence time and mixing parameters as summarized by the Peclet number and eddy diffusivity have been obtained and their significance and limitations discussed. Values of the mass transfer coefficient, kLa obtained from the efficiency studies varied between 0.091 and 0.147 sec-1 for the round column and 0.139 and 0.25 sec-1 for the rectangular column, over the range of operating variables investigated. The studies establish more clearly the significance of large diameter perforations in the context of tray performance and fill a gap in the knowledge of the performance of such hole sizes. Results have been correlated wherever possible in a form suitable for design purposes.