* Regulators in early stages of probe on how Google handles some ad sales -source

* Inquiry focuses on tools acquired with purchase of DoubleClick -source

WASHINGTON, May 23 (Reuters) - U.S. regulators are in the early stages of an antitrust probe into whether Google Inc , the top player in Web display advertising, breaks antitrust law in how it handles some advertising sales, a source told Reuters on Thursday.

The source said that it was unlikely that the Federal Trade Commission had sent out civil investigative demands in relation to the probe, which would be the sign of a formal and more serious investigation.

The new line of inquiry focuses on tools acquired when Google bought display ad company DoubleClick in 2007; other firms which specialize in helping Web publishers sell ads to put on their websites are complaining to the FTC, the source said.

The firms have accused Google of leveraging some of its most popular DoubleClick products, such as the ad managing system which has an estimated 80 percent of the market, to push websites to use other products, including Ad Exchange where websites swap ads, the source said.

According to a second source familiar with the situation, Google has not been notified of any antitrust investigation so far. Google and the Federal Trade Commission declined comment on the matter.

The sources did not want to be named in order to protect their business relationships.

The FTC wrapped up an earlier investigation into Google just four months ago, concluding that the search giant had not manipulated its Web search results to hurt rivals.

Google was the number one player in the $15 billion U.S. display ad market in 2012, with a 15.1 percent market share, compared with Facebook Inc's 14.6 percent share, according to industry research firm eMarketer. Google is expected to widen its lead to 20.7 percent of the market in 2014.

Google is currently trying to convince European antitrust investigators to wrap up a separate antitrust probe, and has offered to change some search pages to give more space to rivals in order to satisfy their concerns.

In that case, Google is accused of hiding links to rival shopping, travel and other websites to protect its ad revenues. On April 11, it said it would offer consumers links to three rival sites in some searches and would label its products.

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  • #6 - ITA Software ($700 million)

    <strong>What people said...</strong> <a href="http://www.bloomberg.com/news/2010-04-21/google-said-to-be-in-talks-to-buy-travel-software-maker.html" target="_hplink">Henry Harteveldt</a>, analyst at Forrester Research: "Google's mission is to organize the world's information, and ITA does that for travel" <a href="http://hasbrouck.org/blog/archives/001881.html" target="_hplink">Edward Hasbrouck</a>, author and policy analyst for Consumer Travel Alliance: "Google's purchase of ITA Software is likely to be a bad thing for travelers." <strong>Acquired: 2010</strong> <em>Source: <a href="http://googleblog.blogspot.com/2010/07/taking-off-with-ita.html" target="_hplink">Google Blog</a></em>

  • #5 - AdMob ($750 million)

    <strong>What people said...</strong> <a href="http://www.nytimes.com/2009/11/10/technology/companies/10google.html" target="_hplink">Neil Strother</a>, analyst at Forrester Research: "The deal shows that Google is serious about becoming a major player in the mobile advertising ecosystem" <a href="http://www.nytimes.com/2009/11/10/technology/companies/10google.html" target="_hplink">Marc Rotenberg</a>, executive director of the Electronic Privacy Information Center: "We've reached a point in Google's evolution in which Washington agencies and Congressional committees need to look more closely at the company's dominance of Internet services" <strong>Acquired: 2010</strong> <em>Source: <a href="http://googleblog.blogspot.com/2010/05/weve-officially-acquired-admob.html" target="_hplink">Google Blog</a></em>

  • #4 - Waze ($1.1 Billion)

    Google <a href="http://allthingsd.com/20130611/google-officially-closes-waze-deal-will-keep-it-independent" target="_hplink">bought mapping startup Waze</a> for $1.1 billion on June 11, 2013, AllThingsD reports.

  • #3 - YouTube ($1.65 billion)

    <strong>What people said...</strong> <a href="http://www.marketwatch.com/story/google-buying-youtube-for-165-bln-as-street-cheers" target="_hplink">Goldman Sachs</a>: "We expect investors to be excited by the strategic opportunities, but they will be skeptical of the $1.65 billion price, given YouTube's early stages" <a href="http://money.cnn.com/2006/10/09/technology/googleyoutube_deal/" target="_hplink">Martin Pyykkonen</a>, analyst at Global Crown Capital: "I would think that a lot of advertisers would be willing to pay a premium for a video search ad opposed to paid search text" <strong>Acquired: 2006</strong> <em>Source: <a href="http://www.google.com/press/pressrel/google_youtube.html" target="_hplink">Google</a></em>

  • #2 - DoubleClick ($3.1 billion)

    <strong>What people said...</strong> <a href="http://www.wired.com/epicenter/tag/doubleclick/" target="_hplink">Federal Trade Commission</a>: "The FTC lacks the legal authority to block the transaction on grounds, or require conditions to this transaction, that do not relate to antitrust" <a href="http://www.wired.com/epicenter/tag/doubleclick/" target="_hplink">Jeff Chester</a>, executive director of the Center for Digital Democracy: "The FTC is supposed to protect the privacy of Americans in the digital age. The excuse offered by the majority of the commission-that consumer privacy can't be addressed by current antitrust law-reveals a lack of leadership and determination to protect U.S. consumers" <strong>Acquired: 2008</strong> <em>Source: <a href="http://googleblog.blogspot.com/2008/03/weve-officially-acquired-doubleclick.html" target="_hplink">Google Blog</a></em>

  • #1 - Motorola Mobility ($12.5 billion)

    <strong>What people are saying...</strong> <a href="http://www.businessinsider.com/google-motorola-deal-2011-8" target="_hplink">Henry Blodget</a>, editor-in-chief at Business Insider: "This deal could end up being a disaster" <a href="http://www.huffingtonpost.com/jeff-jarvis/google-buys-rat-poison_b_927155.html" target="_hplink">Jeff Jarvis</a>, author: "Google buys rat poison" <a href="http://www.telegraph.co.uk/technology/google/8702125/Google-buys-Motorola-Mobility-market-reaction.html" target="_hplink">Hendi Susanto</a>, analyst at Gabelli & Co: "Google and Motorola will create a stronger hardware - software integration to compete with Apple, Samsung, and HTC." <strong>Acquired: 2011</strong> <em>Source: <a href="http://googleblog.blogspot.com/2011/08/supercharging-android-google-to-acquire.html" target="_hplink">Google Blog</a></em>