Mass-transfer characteristics were measured for the Mellapak structured packing series 250Y, 350Y, 452Y, and 500Y. k(L)a was measured by oxygen desorption from water and the effective mass-transfer area a by absorption of CO2 into NaOH solution and also by oxygen absorption into a sulfite solution. Using Bodenstein numbers determined by means of the "cold" air-water dynamic experiments, effects of gas- and liquid-phase axial mixing on the characteristics were evaluated for Mellapalc 250Y. Strikingly large differences found between the mass-transfer parameters and their flow dependencies measured in this work and those predicted by models especially designed for the prediction of the parameters in corrugated sheet structured packings (Billet, R.; Schultes, M. Chem. Eng. Res. Des. 1999, 77, 498; Rocha, J. A.; Bravo, J. L.; Fair, J. R. Ind. Eng. Chem. Res. 1996, 35, 1660; Olujic, Z.; Kamerbeek, A. B.; Graauw, J. Chem. Eng. Process. 1999, 38, 683) demonstrate the bad physical relevance of the parameters predicted.