Commercial's total share fell from 45.5 per cent in the first quarter of 2004 to 43.8 per cent this year. The BBC's share increased to 54.2 per cent.
However, thanks to strong performances from digital stations and the likes of Virgin Radio, national commercial radio increased its share of listening from 9.9 to 10.2 per cent year on year.
Virgin Radio and talkSPORT grew their share of listening but Classic FM's share was down.
Peter Cory, the media planning director at the Radio Advertising Bureau, said: "The results reported little overall change for commercial radio quarter on quarter in total hours and reach, but delivered longer-term positive trends against key advertiser demographics such as housewives and young people."