Various methods have been used to deduce HETP values from absorption mass transfer data for a number of packings and comparisons made with HETP values obtained by distillation experiments on the same packings. Volumetric gas-film and liquid-film mass transfer coefficients in gas and liquid and interfacial areas were measured for metal Pall Rings (25 and 50 mm), metal mesh S-packing 25/30 mm and the structured glass packing Combi-Pack 250, using the absorption systems SO2/air-1M NaOH, O-2/air-water and CO2/air-1M NaOH. Using these directly gave individual mass transfer film-coefficients for both phases. Five different procedures based on the Onda et al. and Billet et al. correlations were used to transform absorption mass transfer data to HETP for the atmospheric distillation of benzene-toluene and methanol-ethanol, and for vacuum distillation of chlorobenzene-ethylbenzene and ethylbenzene-styrene. The best results (agreement within +/-15%) were obtained by the simple transformation based only on difference in diffusivities for the absorption and distillation systems : k(G) approximate to D-G(2/3), k(L) approximate to D-L(1/2). It seems that the influence of other physical properties such as density, viscosity and surface tension are not well established in the correlations when large extrapolation is needed.