The potential investor upside of a Google breakup — if John Rockefeller is any guide

Google's (GOOG, GOOGL) legal troubles could force it to sell off some of its prized businesses, but investors worried about that outcome may find some comfort in what happened to John Rockefeller’s Standard Oil more than a century ago.

The empire that controlled nearly all US oil production during America’s industrial revolution had to split into 34 smaller companies after the Supreme Court in 1911 sided with the Justice Department in an antitrust challenge.

The divestiture of those companies made Rockefeller the richest man in the world. But it also made other shareholders in those new companies richer too, according to legal experts.

The companies became giants such as Chevron (CVX) and Exxon Mobil (XOM) that still rule the industry today.

“[T]he market cap total for all those companies increased about five- to six-fold based on what the valuation was thought for Standard Oil,” said Boston College Law School antitrust law professor David Olson.

New management and efficiencies that followed the breakup helped the smaller companies flourish, added Susman Godfrey antitrust litigation attorney Barry Barnett.

In the case of Google, existing shareholders may benefit as a scaled-back company tends to boost innovation and customer service, Barnett said. Google's search engine, for example, could start producing more relevant results and become more valuable to advertisers.

"The people who own the company are not going to lose," Barnett said.

Not everyone agrees with this rosy view. One analyst at Evercore ISI recently reduced a price target on Alphabet, Google’s parent company, after rereading a federal judge’s landmark US antitrust ruling against the company handed down in August.

US District Court Judge Amit Mehta, who decided the case, sided with the US Justice Department’s claims that Google’s Search business was an illegal monopoly that it abused to keep rivals at bay.

Mehta also agreed with the DOJ’s accusations that Google illegally monopolized the market for online search text advertising.

"[W]e believe a ‘worst case’ scenario is a more likely scenario than the market assumes," Evercore’s analyst wrote in the note.

It is not yet known what remedies the judge may approve as a result of his ruling.

They could range from an outright breakup of Google to forcing the company to make its search engine data, its "index," available to competitors.

It could also be forced to end the types of agreements that got Google into trouble with regulators, that secure its search engine as a default on mobile devices and internet browsers.