It has recently been demonstrated that spectral-domain models of wave energy converters (WECs) can provide an accurate and numerically efficient method for predicting the expected performance of WECs. An oscillating water column (OWC) type WEC has been tested in a wave tank to produce validation data for a spectral-domain model of the OWC. The OWC spectral-domain model consists of linear hydrodynamic coefficients obtained from the commercial boundary-element code WAMIT, together with single-coefficient non-linear terms for the power-take-off (PTO) and the entry/exit losses of the water column. The OWC was tested in a range of representative sea-states with both unimodal and bimodal spectra. The coefficients for the PTO and entry/exit losses were determined using the orifice pressure/flow characteristics and a single calibration sea-state respectively. Comparison of the OWC spectral-domain model with the wave-tank data indicates that the spectral-domain model reproduces the performance of the OWC accurately. The error in spectral-domain model’s prediction of power capture is typically less than 5%. The frequency response of the OWC is also well predicted by the spectral-domain model. This demonstrates that a spectral-domain model provides a valid representation of the wave-tank OWC model performance.