Just six months ago, Pandora's Average Active Sessions, something like broadcast radio's Average Quarter Hour statistic, were about 682,000. In the just-released November Triton Digital rankers, Pandora becomes the first Internet audio service to crack the one-million mark, with a measured 1,045,551 sessions. The "Session Starts" figure, somewhat comparable to the traditional cume or reach figure, is much larger for Pandora: 416 million. #5-ranked Slacker, another Internet audio service that also now includes AOL Radio, shows continued growth. Its Average Active Sessions grew from October's 48,526, to November's 63,568. Its Session Starts grew from 17,458,464 to 21,118,129.

Clear Channel, with its iHeartRadio re-launch in September, grew from 162,093 Active Sessions to 168,173. Its Sessions Starts improved much more, from about 62 million to 71.4 million. CBS Radio, which recently ended its association with AOL Radio, dropped in both Active Sessions (from 126,538 to 97,107) and Session Starts (from about 36 million to 28.9 million). Read Triton Digital's Top 20 rankers, including the ones quoted here for "Domestic" (U.S. Only), 6am to 8pm weekdays, here.