Google has broken into radio with a multi-year advertising sales agreement with the largest U.S. broadcaster, Clear Channel Radio. Clear Channel said it has agreed for Google to sell a guaranteed portion of the 30-second spots available on its 675 radio stations in top U.S. markets, in a bid to expand the universe of local radio advertisers to Google’s online buyers.

A Clear Channel executive said Google has access to less than 5% of the radio broadcaster’s overall inventory of advertising air time. The U.S. radio industry generates $20 billion in annual sales. [USAToday]