Google is locked in a six-year battle with Europe's antitrust officials. And the stakes for both sides are getting higher.

For Google, Europe’s lengthy effort to rein in how the search giant operates in the region represents a potential threat to the billions of dollars it earns annually from selling online advertising and other, often dominant, digital services across the Continent and beyond.

For Margrethe Vestager, the Danish politician turned European competition chief, the three cases against Google make up the most public — and longstanding — antitrust cases in the region. And they will very likely define Europe’s at times frosty relationship with Google and other American tech giants like Facebook, Amazon and Apple for years to come.

“For the European Commission, it’s a case of Russian roulette,” said Christian Bergqvist, an associate professor of competition law at the University of Copenhagen. “If they lose or merely settle the case, they will look weak. They have to be seen as doing something to stop Google.”