Distillation is the most important thermal separation process, with separation efficiency as one of the fundamental parameters to influence economy and energy consumption. The precise knowledge of separation efficiency and the ability to compare different types of column internals is vital information for the chemical industry. Still, total reflux distillation experiments are the only significant source of such data. The authors have taken the effort to work out in elaborate manner different factors influencing both measurement and interpretation of structured packing separation efficiency data, to provide basis for establishing an open standard in this respect. In addition, an improved set of thermophysical correlations for the test system chlorobenzene/ethylbenzene (CB/EB) is presented. (C) 2011 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.