Data on the rate of liquid-phase controlled mass transfer in a small-diameter tube (ID 4 mm) are presented. The motivation is to model the performance of compact contact devices consisting of short, narrow passages. The mean volumetric mass transfer coefficient, K(L)a, is measured for a wide range of superficial gas and liquid velocities (U-GS = 0.1-30 m s(-1) and U-LS = 0.01-1 m s(-1)). Results are related to flow regime transitions and are correlated in terms of Jepsen’s (1970, A.I.Ch.E. J. 16, 705-711) fractional energy dissipation parameter.