This paper presents the results of a blade-element aerodynamic simulation of reversible axial flow air turbines designed to service Oscillating Water Column (OWC) ocean wave energy systems. The first section of the paper presents a new approach to the “blade element” analysis of such devices wherein an actuator disc/blade-element analysis is formulated purely in terms of non-dimensional variables (ie flow factor, blade lift/drag data, angle of attack, etc). The non-dimensional pressure drop, torque, input and efficiency coefficients are determined using this numerical model for both Wells Turbines and for a variable-pitch turbines such as the Denniss-Auld turbine developed by Oceanlinx (Australia). The results of the blade-element simulation with and without the inclusion of “interference effects” of neighbouring blades in the cascade of blades in the rotor are then presented. The importance of correct modelling of these interference effects is demonstrated through the significant effects on the efficiency, torque coefficient and pressure drop through the turbine. The implications for the optimisation of OWC air turbine designs through modification of the blade element method is discussed and commentary is provided on the matching of the turbine to the required optimal pneumatic damping of the oscillating water column chamber.