Large sea level oscillations (up to 1-m amplitude and around 10-min period) have been observed in several bays and harbors of the western Mediterranean. These oscillations appear to be associated with short-period (10 min) atmospheric pressure fluctuations (amplitude of 1.5 mbar). Using a model with a flat shelf and a sloping-bottom harbor, we found that these oscillations were the result of a three-way resonant coupling between an atmospheric gravity wave, a coastally trapped edge wave, and the normal modes of a harbor. The amplification mechanism was studied for the harbor of Ciutadella. Good agreement between the predicted and the observed frequencies and amplitudes is found. ¿ American Geophysical Union 1988