Radio ad revenues fell 7% in September 2007 compared with September 2006, according to a MediaPost report.

The publication said that ad revenue in the top 25 radio markets fell 4% in September, and that revenue in mid-sized markets fell 6%.

Small-market radio stations had better revenue performance for the month, but revenue growth for such stations is now almost flat.

As a result of the news, some analysts are now revising their forecasts for the second half of 2007. Among these are CL King and Associates, which now predicts a 3% revenue drop for the third quarter.

MediaPost suggested that an economic downturn could produce especially grim results for radio ad revenue in the last quarter of the year.