The songs of 8 male humpback whales were recorded at ranges varying from 20 to 40 m with a calibrated system that had a flat frequency response to 22 kHz. The songs consisted of bursts of sounds called units. Units were organized into phrases and phrases into themes. Most of the units had mean duration between 1 and 2 s and mean silent periods between units between 1 and 2 s. Many of the recorded songs contained units that had high-frequency harmonics that extended beyond 15 kHz. The amplitudes of the higher-frequency harmonics of some units were within 18–24 dB of the fundamental or the highest level harmonic at frequencies out to 13.5 kHz. These harmonic results suggest that humpback whale songs have a broadband quality not previously reported and may provide some insights on the high-frequency limit of hearing in these whales. The source levels of the different songs were also estimated by considering the root mean square sound pressure level referenced to 1 m for the unit with the largest level for each different phrase within a song. Source levels varied between 171 and 189 dB re: 1 μPa.