Time-dependent laminar flow in a continuous oscillatory baffled reactor has been studied using Computational Fluid Dynamics. The effect of baffle geometry on pressure drop, energy dissipation as well as the instantaneous flow and shear strain rate fields has been investigated for five different geometries, namely single orifice baffles, disc-and-donut baffles and three novel variations of helical blades. All designs show complex flow behaviour and the formations of vortices due to both flow blockage and flow reversal with various amounts of pressure drop and energy dissipation. However, it is clearly difficult to conclude on the impact of baffle design on the performance of the reactor with velocity, shear strain rates and vorticity alone. Part II of the paper therefore presents and exploits alternative quantitative measures to better quantify reactor performance. (C) 2016 Elsevier B.V. All rights reserved.