Broadband, high-fidelity recordings of blue whale calls are used to model parameters of the sound generation mechanism. Arrays of sonobuoys have been used to characterize and localize calling whales, providing broadband (10–2400 Hz), high dynamic range (90 dB) recordings. Blue whales typically produce 15- to 20-Hz sounds of up to 30-s duration at levels of 185 dB re: 1 μPa@1 m. The observed sound levels, frequencies, and harmonic content have implications for the sound generation parameters. Source levels provide constraints on volume displacements. Frequencies and harmonic content relate to resonant structures and their means of excitation. The data show harmonic series with selected overtones emphasized. The relative amplitudes of the overtones vary between different parts of the call.