We report, for the first time, our direct experimental measurement of velocity vectors and strain-rate distributions in an oscillatory baffled column (OBC) using time-resolved particle image velocimetry (PIV). The technique allowed a time series of spatial velocity maps to be obtained for several phases per oscillation cycle and the results, comprising several thousand such maps, illustrate in detail the variations of velocity and strain rate in a baffled region over a range of oscillation amplitudes and oscillation frequencies and provide a deep insight into the mixing, vortex convection and transport mechanism in such a device. The results show that an OBC not only provides enhanced mixing, but also offers low strain rates, which are lower than those in stirred tank vessels. We have also reported for the first time the quantitative correlation between the strain rate and the power dissipation in an OBC. Using the PIV technique we are able to quantify the strain rates experienced in an OBC,