Normalized energy density spectra were obtained from the tide‐gauge records of Concepción Bay (Chile) for March 10, 1957, May 22, 1960, and March 28, 1964 tsunamis. Distribution of energy peaks with frequency is explained by means of a rectangular bay. resonant model, and are identified as the first, second, and third harmonic modes of oscillation. For the 1960 tsunami, amplification factors computed from offshore sea surface elevation predictions agree reasonably with the values given by the model.