Just hours after saying it ended talks of a possible investment with Microsoft, Yahoo announced a deal with Google to run some of Google's advertisements alongside Yahoo search results.

The nonexclusive deal unites the online advertising businesses of Google and Yahoo and comes as a setback to Microsoft, which had been trying to acquire all or part of Yahoo to strengthen its own online business and compete better with Google.

Yahoo said it expects the deal to generate $250 million to $450 million in operating cash flow during the first 12 months, and that it represents an annual revenue opportunity for Yahoo of $800 million. The deal is for an initial period of four years, with an option for Yahoo to extend it for a further six years.

The deal was announced after Yahoo said earlier on Thursday that it had ended its talks with Microsoft over a possible investment by the software giant. Yahoo said it ended the talks because Microsoft was interested only in acquiring Yahoo's search business, not the entire company.

"Clearly it is time to move on," Yahoo CEO and cofounder Jerry Yang said during a conference call. "We believe this agreement with Google helps us to do so by strengthening our competitive position and generating attractive financial benefits."

Yang and Sue Decker, Yahoo's president, said the deal will allow Yahoo to capitalize on growth in the online advertising market and "the convergence of search and display advertising."

They emphasized the flexible terms of the deal for Yahoo. Yahoo will be able to choose the search term queries for which Google's advertisements will appear, and also the pages on which they appear. The deal applies to the U.S. and Canada only and is nonexclusive, so Yahoo could cut deals with other companies and can also keep selling ads from its own Panama advertising platform.

Advertisers will pay Google for its ads that appear by Yahoo searches, and Google will then pay a portion of the revenue to Yahoo, Decker said. "We improve our access to the paid search universe, but on terms that work for us," she said.

While this deal isn't quite as good as a Microsoft acquisition for Yahoo's investors, it's the next best thing, said Greg Sterling of Sterling Market Intelligence. "While it's no substitute for an outright acquisition from Microsoft in terms of shareholder value, this is probably smart for [Yahoo] provided they invest in their own platform," he said.

Continuing to develop Panama will be key to Yahoo's future, Sterling said. "If they get lazy about it and start to turn over more and more to Google because they have the inventory and neglect their own platform, that could over time erode the position of Panama," Sterling said. "So they have to be vigilant about that."

As part of the deal, the companies also plan to make their instant-messaging services interoperate, Decker said.

Yahoo and Google had been in talks over a potential deal for months. It was seen as a way for Yahoo to strengthen its advertising business and alleviate the pressure to be acquired by Microsoft. Microsoft had cited any deal with Google as a potential deal-breaker in its talks with Yahoo. It had also called it a bad business decision that would only serve to strengthen Google, the online ad market leader.

Yahoo and Google said they don't require regulatory approval for the deal, but that they would delay its implementation for three-and-a-half months while the U.S. Department of Justice reviews the arrangement. Various groups ranging from farmers to Microsoft have expressed concern about such a deal.

The deal doesn't mark the end of the turmoil around Yahoo. Its board faces a proposal by billionaire investor Carl Icahn, who hopes to replace the entire board in order to force a deal with Microsoft.

However, the announcement probably spells the end of Icahn's plan, according to Sterling. Shareholders would only be inclined to vote for Icahn's proposed board if they think it would help force a sale to Microsoft, Sterling noted. But Microsoft has said that it isn't interested in buying all of Yahoo, only its search business. That kind of deal would leave the remaining Yahoo in a much worse position than it is now, he said.

This story was updated on June 12, 2008