Most descriptions of sounds produced by whales at sea have been described from scattered, unsystematic observation and recording of animals during shipboard encounters. Such encounters provide data on only a few individuals in isolated locations. Since the original scientific recordings of cetaceans by Schevill and Lawrence (1949, 1950), about 70 species have been recorded and calls catalogued (Schevill and Watkins, 1962; Watkins and Wartzok, 1985; Watkins et al., 1991). These include calls recorded close to whales and those monitored remotely over extended periods from the three species whose sounds are analyzed here: blue whales, (Balaenoptera musculus, Cummings and Thompson, 1971; Thompson and Friedl, 1982; McDonald et al., 1995; Clark and Fristrup, 1997; Rivers, 1997) fin whales (Balaenoptera physalus, Schevill et al., 1964; Watkins, 1981; Thompson and Friedl, 1982; Watkins et al., 1987), and humpback whales (Megaptera novaeangliae, Payne and McVay, 1971; Tyack, 1981; Payne et al., 1983). These previous studies provided the basis for confident recognition of the calls of these species.