For the first time in December, the nation's top internet radio networks' total audience exceeded seven million weekly listeners, according to comScore Arbitron's latest report, writes MediaWeek (via MediaBuyerPlanner). Also a new high, the average midday audience for five of the top networks - including AOL Radio Network, Yahoo Music's Launchcast and Clear Channel Online Music and Radio - surpassed 1.8 million listeners.

Webcast Metrics, which provides third-party audience data for a smaller collection of internet radio stations, reported that the average monthly audience for these stations is between six and seven million per week.

A year ago, Arbitron released a report that during an average week an estimated 20 million Americans listened to internet radio.