The mass-transfer area of nine structured packings was measured in a 0.427 m ID column via absorption of CO 2 from air into 0.1 kmol/m 3 NaOH. The mass-transfer area was most strongly related to the specific area (125-500 m Áh). Surface tension (30-72 mN/m) had a weaker but significant effect. Gas velocity (0.6-2.3 m/s), liquid viscosity (1-15 mPaÁs), and flow channel configuration had essentially no impact on the mass-transfer area. Surface texture (embossing) increased the effective area by 10% at most. The ratio of mass-transfer area to specific area (a e /a p ) was correlated within the limits of AE13% for the entire experimental database a e a p ¼ 1:34