This paper is concerned with the fluid mechanics and mixing performance of a novel oscillatory flow screening reactor. Using fibre optic probes, a mixing coefficient km is determined for the system as a function of the applied fluid oscillation frequency and amplitude. In a continuous operation mean residence time and a backmixing coefficient g are estimated as a function of the oscillation conditions. Finally, in order to compare data with numerical simulations steady state flow data are also included. The screening reactor presented an intermediate mixing behaviour throughout all the studied range of oscillation amplitudes (0-3 rum centre-to-peak) and frequencies (0-20 Hz). The backmixing was found to be highly dependent of the oscillation frequency and amplitude. Nevertheless, a stronger effect of the oscillation amplitude over the axial dispersion was detected presumably due to the increase of the mixing length. On the other hand, the increase of the oscillation frequency was concluded to have the increase in the radial mixing rates as the main effect. Thus, it was possible to achieve a decrease in the axial dispersion with the screening reactor using oscillatory flow, when compared to the laminar steady flow in a plain tube with the same mean internal diameter. (C) 2004 Elsevier Ltd. All rights reserved.