The effect of scale-up on air-water mass transfer in oscillatory multiorifice baffled reactors (OMBRs) was investigated. Reactors of 10, 50, and 100 mm diameter were studied. The reactors had the same aspect ratio, dimensionless baffle spacing, open cross-sectional area, and orifice diameter. Air-water flow patterns were visualized using a high-speed camera, and the k(L)a was determined on the basis of dissolved gas measurements. On the basis of these results, a dimensionless scale-up correlation, based on Sh, Re-o (the oscillatory flow Reynolds number), Re-G (the superficial gas velocity Reynolds number), and the diameter ratio, was developed and successfully validated against this data and literature values.