Google — whose profitability was realized in great part by its sponsored search and text ad business — is making inroads into the graphical display ad market, an arena dominated by Yahoo, The New York Times reports.

Today the search giant introduces the new version of a stock market-style ad exchange, where advertisrs and publishers can buy and sell ad space as they please. This model would enable them to fill remnant inventory with greater speed.

The model is an old one. Late last year Platform-A launched BidPlace under a similar premise. There is also ContextWeb's ADSDAQ.

Google's own ad exchange has been in the works for some time. It was one of the company's primary reasons for purchasing DoubleClick last year for $3.1 billion.

The system will be dubbed the DoubleClick Ad Exchange, and its objective will be "to grow the display advertising pie for everybody,” said VP-Product Management Neal Mohan of Google.

The new system builds on DoubleClick's existing ad exchange by allowing the hundreds of thousands of advertisers and publishers on Google's AdWords and AdSense system to access the platform. This significantly expands the breadth of DoubleClick's exchange system, and enables brand advertisers to run campaigns that reach nearly the entire online population.

"Marketers are going to be able to effectively reach 100 percent of the Internet audience and do so at a high frequency," said ThinkEquity Partners analyst William Morrison. "That is very difficult to do on the Internet right now, outside of a handful of major Web sites like Yahoo and a few others."

For its part, display ad rival-to-be Yahoo remains collected. "We will continue to innovate and do our best to control our own destiny," stated VP-North American market Frank Weishaupt.

Presently, ad exchanges only account for around 10-15% of the display ad business.