Theroretical predictions of sea surface reverberation are compared with representative acoustic and radar data to determine those mechanisms responsible for backscatter. Predictions of the composite roughness scattering model are compared with data in three frequency ranges, 2--5 kHz acoustic (428- and 1228-MHz radar), 20--25 kHz acoustic (4455-MHz radar), and 58--60 kHz acoustic (8910-MHz radar). The predicted backscattering strength is found to be in relatively good agreement with the radar data at all frequencies; however, only at the lowest frequency do the predictions match the acoustic data. At the two higher frequencies, the measured acoustic backscatter greatly exceeds the composite roughness predictions at low grazing angles. To account for this discrepancy, a simple model is used to compute the reverberation due to a near-surface bubble layer. The computed bubble contribution is shown to provide good agreement with the acoustic data and also to predict the saturation that occurs with increasing wind speed.