Breakup of Google’s Ad Business Would Reshape $500 Billion Sector

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If government prevails, an asset spinoff is thought to be more likely than a sale

Splitting up Google’s ad business would potentially give publishers and advertisers more choice.

Google spent the better part of two decades building the world’s most powerful digital advertising machine. Breaking it up would send shock waves through the $500 billion online-ad market.

If the U.S. government wins the antitrust lawsuit it filed last week and the Alphabet Inc. internet company is required to spin off technology for brokering ad deals across the web, the separated businesses would be valued at tens of billions of dollars, according to ad and media-industry executives.