Aug. 14 (Bloomberg) -- The biggest U.S. media companies and advertisers are in talks to develop a system that would challenge Nielsen Co.’s audience ratings, according to three people with knowledge of the situation.

Work on a system to measure television and Web viewing may begin as early as next month, said two of the people, who asked not to be named because the talks are private. The owners of the four largest broadcast TV networks, ABC parent Walt Disney Co., General Electric Co.’s NBC Universal, CBS Corp. and Fox parent News Corp., are involved, the people said.

Nielsen, whose audience data help set advertising prices, is trying to track Web and mobile device viewers as well. TiVo Inc. and other companies are also challenging Nielsen, said Porter Bibb, managing partner at New York-based Mediatech Capital Partners LLC, which advises media and technology companies. None have succeeded because of costs, he said.

“With the changing distribution and fragmentation of all the media, Nielsen is still going to reign supreme,” Bibb said today in a Bloomberg Television interview.

Details of the measurement system are still being worked out, according to the people. The Financial Times reported on the talks earlier.

The discussions also include Time Warner Inc., Viacom Inc. and Discovery Communications Inc., the operators of ad-supported cable channels, the people said.

Companies involved on the advertising side include Procter & Gamble Co., AT&T Inc. and Unilever, and the media-buying companies GroupM and Starcom MediaVest, the people said.

TV Ad Spending

Keith Cocozza, a spokesman for New York-based Time Warner, declined to comment, as did Gil Schwartz of CBS, Mark Jafar of Viacom’s MTV Networks, Discovery’s Alison Rudnick, Teri Everett of News Corp., Julie Hoover of Disney’s ABC, AT&T’s Michael Coe, Dean Mastrojohn of Unilever and Barbara Hauser of P&G.

Representatives of New York-based NBC, GroupM, Starcom and Nielsen didn’t respond to requests for comment.

Spending on U.S. television advertising this year will fall about 12 percent to $60.1 billion, Michael Nathanson, a New York-based analyst with Sanford C. Bernstein & Co., estimated in a research note yesterday. Marketers will earmark $22.7 billion for Internet ads this year, he projected.

Nielsen has been building a measurement system to include TV, the Web and mobile products at the request of clients, Chief Financial Officer Brian West said on the company’s earnings conference call yesterday. Closely held Nielsen has a headquarters in New York and Haarlem, Netherlands.

‘Good Position’

“We’re in a world where there’s going to be lots of competitive folks out there looking to get more precise analytics around audience measurement,” West said. “We think that we’re in a pretty good position to be able to be successful.”

Burbank, California-based Disney, the world’s biggest media company, fell 40 cents to $25.86 at 4 p.m. in New York Stock Exchange composite trading. New York-based CBS, owner of the most-watched U.S. TV network, dropped 6 cents to $10.23.

Cincinnati-based P&G, the world’s largest advertiser, gained 7 cents to $52.37. AT&T, located in Dallas, fell 3 cents to $25.45.

To contact the reporters on this story: Sarah Rabil in New York at srabil@bloomberg.netAndy Fixmer in Los Angeles at afixmer@bloomberg.net

Last Updated: August 14, 2009 17:03 EDT