The performance of an oscillating water column wave energy converter is investigated based on both numerical and experimental approaches. The viscosity effects are neglected in the numerical approach and the boundary integral equation method (BIEM) is implemented to solve the appropriate 2D boundary value problem (BVP). The influence of turbine damping and wave period is evaluated in the numerical model in both regular and random waves. A comprehensive experimental campaign is carried out in both regular and irregular waves to validate the numerical results as well as to investigate the influence of wave height, period and turbine damping on the efficiency of the converter. High and low turbine damping conditions are imposed to the experimental model. It is found that both the numerical and experimental results have a satisfactory agreement for the small wave amplitudes. It is detected that the efficiency of the device is very sensitive to the variations in the turbine damping although the absolute maximum efficiency is less sensitive to the slight alterations applied to the turbine damping. It is observed in the experimental study that the influence of the wave height has less importance than the other two parameters (turbine damping and incoming wave period) although the effect of the wave height becomes prominent in high wave amplitudes and causes the efficiency of the device to become less sensitive to variations in wave period and to tend to have an uniform value in wide wave period ranges.