In a move that extends Nielsen’s monopoly reach on TV ratings to also include the U.S. radio market, the company announced plans today to buy Arbitron for $1.26 billion, Advertising Age reports.

“Nielsen, already by far the largest research company in the world, will add the No. 9 player in the 2012 Honomichl 25 rankings of research companies, creating a company with a combined revenue of around $6 billion — nearly double the $3.3 billion 2011 sales of No. 2 research player, WPP’s Kantar,” the piece reports.

The deal requires regulatory approval, which could be complicated by the fact that Arbitron and Nielsen have been potential competitors for some time, the report notes.