Google has ended its ad partnership with Yahoo, a deal that would have given Yahoo $800 million in annual revenue. This after the companies failed to get support from the U.S. government. 

"It's clear that government regulators and some advertisers continue to have concerns about the agreement. Pressing ahead risked not only a protracted legal battle but also damage to relationships with valued partners," according to a Google statement.

Google stepped in with this search partnership to save Yahoo from a Microsoft offer of $47.5 billion.

Now that it's terminated, one option for Yahoo is to sell its search business to Microsoft.

Microsoft had previously offered $1 billion for Yahoo's search business, according to Imran Khan, an Internet analyst at JP Morgan.

Yahoo could gain an additional $725 million in annual operating cash flow through a Microsoft deal, according to  Khan.

And, if Yahoo sold its search business, it may have cash to make acquisitions, Khan added.

According to Google:

In June we announced an advertising agreement with Yahoo! that gave Yahoo! the option of using Google to provide ads on its websites (and its publisher partners' sites) in the U.S. and Canada. At the same time, both companies agreed to delay implementation of the agreement to give regulators the chance to review it. While this wasn't legally necessary, we thought it was the right thing to do because Google and Yahoo! have been successful in online advertising and we realized that any cooperation between us would attract attention.

We feel that the agreement would have been good for publishers, advertisers, and users -- as well, of course, for Yahoo! and Google. Why? Because it would have allowed Yahoo! (and its existing publisher partners) to show more relevant ads for queries that currently generate few or no advertisements. Better ads are more useful for users, more efficient for advertisers, and more valuable for publishers.

However, after four months of review, including discussions of various possible changes to the agreement, it's clear that government regulators and some advertisers continue to have concerns about the agreement. Pressing ahead risked not only a protracted legal battle but also damage to relationships with valued partners. That wouldn't have been in the long-term interests of Google or our users, so we have decided to end the agreement.

We're of course disappointed that this deal won't be moving ahead. But we're not going to let the prospect of a lengthy legal battle distract us from our core mission. That would be like trying to drive down the road of innovation with the parking brake on. Google's continued success depends on staying focused on what we do best: creating useful products for our users and partners.

From Yahoo

Yahoo! Inc. (Nasdaq: YHOO), a leading global Internet company, today announced that Google has terminated the advertising services agreement the companies announced in June. Yahoo! continues to believe in the benefits of the agreement and is disappointed that Google has elected to withdraw from the agreement rather than defend it in court. Google notified Yahoo! of its refusal to move forward with implementation of the agreement following indication from the Department of Justice that it would seek to block it, despite Yahoo!'s proposed revisions to address the DOJ's concerns.

While the implementation of the services agreement with Google would have enabled Yahoo! to accelerate its investments in its top business priorities through an infusion of additional operating cash flow, this deal was incremental to Yahoo!'s product roadmap and does not change Yahoo!'s commitment to innovation and growth in search. The fundamental building blocks of a stronger Yahoo! in both sponsored and algorithmic search were put in place independent of the agreement.

Yahoo! continually optimizes its algorithmic and sponsored search, and we have, in 2008 alone, developed and launched hundreds of improvements all designed to enhance search quality and deliver a more relevant search experience to the company's users. To that end, Yahoo! has benefited from strong revenue per search (RPS) gains in the U.S. as discussed on the Q3 earnings call. Furthermore, Yahoo! continues to make substantial progress against its Open Strategy and in the deployment of its game changing APT from Yahoo! display advertising platform.

Going forward, Yahoo! plans to continue to provide the cutting-edge advances in products, platforms and services that the industry needs and expects, and intends to be the destination of choice for advertisers and publishers who want to reach one of the largest and most engaged populations of consumers on the web.