This research presents a methodology for carrying out uncertainty analysis on measurements made during wave basin testing of an oscillating water column wave energy converter. Values are determined for type A and type B uncertainty for each parameter of interest, and uncertainty is propagated using the Monte Carlo method to obtain an overall expanded uncertainty with a 95% confidence level associated with the capture width ratio of the device. An investigation into the impact of reflections on the experimental results reveals the importance of identifying the incident and combined wave field at each measurement location used to determine device performance, in order to avoid misleading results.