This paper discusses the benefits of using gravitational oscillations to achieve good mixing in relatively large vessels. An experimental study was performed on a semicircular-type tank equipped with a vertical central baffle plate. Liquid oscillations were generated by a rubber plate, placed on the bottom of the tank, which was divided into two separate chambers that were alternately inflated with controlled compressed air. For specific inflation periods, resonance yielding maximal amplitude was achieved in the two tank compartments. While flow visualization showed overall good mixing for different excitation frequencies, measurements of mixing times via a conductivity method revealed fast mixing for a particular frequency close to the natural frequency of an oscillating U-tube, and for which the maximal oscillation amplitude was recorded.