In the present work the superficial gas velocities (u(G)) and the oscillatory conditions (frequency and amplitude) effects on the gas-liquid mass transfer process in a novel oscillatory flow reactor provided with smooth periodic constrictions (OFR-SPC) are experimentally evaluated. The liquid-side mass transfer coefficient, k(L), and the specific interfacial area, a, are studied individually. The specific interfacial area is obtained using the new automatic image analysis technique developed by Ferreira et al. (2012). The experimental results of volumetric liquid side mass transfer coefficient (k(L)a), Sauter mean diameter (d(32)) and gas holdup (epsilon(G)), and the calculated values of a and k(L), are correlated with the superficial gas velocity and the power density (P/V), in order to be used in scale-up processes and in comparisons with the literature. The results show that k(L)a increases with both superficial gas velocity and oscillatory conditions, the last ones having the highest impact on the mass transfer process. The increase in the oscillation motion (frequency and amplitude) results in bubble size reduction (from similar to 7 mm, without oscillation, to 1 mm, with oscillation), in bubble average residence time increase and, consequently, in a increase. A k(L) increase with d(32) decrease is observed, showing the importance of hydrodynamic phenomena on k(L), specially, when very low bubbles sizes are presented in oscillatory flow reactors. (C) 2014 Elsevier B.V. All rights reserved.