The function of humpback whale song remains elusive. Humpbacks primarily sing on the wintering grounds. Many hypotheses suggest a male advertisement function. It has been suggested that all whales of a population sing the same version of song, and its structure slowly evolves during and between singing seasons. Field observations of 1989 song indicated substantial variation in the song of humpbacks. The question remained, were the differences between individuals greater than those between successive songs of an individual. The songs of 11 whales were sampled during an 8 day period, to reduce the probability that song evolution would affect the results. Six units from three themes were sampled from four songs from each whale. Unit duration, lowest frequency, bandwidth, frequency of peak amplitude, and source level were measured. A repeated measures ANOVA found significant differences between individual whales and no such differences were found between successive songs of the same individual. These data indicate that there are real measurable differences between the songs of different individual whales. These individual differences could be used as a basis for female choice of males, based on song features. While this remains untested, these data are necessary for such a hypothesis.