Humpback whales produce cyclical sound sequences (called songs) that are composed of a variety of structured sound patterns. Past studies of sound patterns and individual sounds within songs have often assumed they are functionally homogeneous elements that are varied to convey information about the singer. Alternatively, differing sounds and sound patterns within songs may be functionally heterogeneous elements that vary for reasons unrelated to information content. To assess this possibility, humpback whale songs recorded in Hawaii from 1992-1995 were analyzed to determine whether whales consistently used some sound patterns more extensively than others and to measure the stability of the acoustic features of sound patterns. It was found that some patterns were consistently produced for long periods of time and that other patterns were consistently produced for short periods of time; acoustic features of both classes of sound patterns were highly stereotyped. The potential detectability of different sounds and sound patterns within songs was found to vary substantially. It is speculated that differences in detectability reflect differences in utility. Finally, in contrast to previous reports, comparisons of the sound patterns analyzed in this study with those described in past studies suggest that several sound patterns recur across years and populations.