Google Inc. may skirt the most serious antitrust allegations under investigation by the U.S. as regulators waver on whether they can prove consumers are hurt by the way the company ranks its search results, three people familiar with the matter said.

Federal Trade Commission officials are unsure they have enough evidence to sue Google successfully under antitrust laws for giving its own services top billing and pushing down the offerings of rivals, said the people, who asked for anonymity because the discussions aren't public. Regulators are also looking at whether the ranking system's benefits to consumers outweigh any harm suffered by rivals including NexTag Inc. and Kayak Software Corp., the people said.

The agency is under pressure to extract concessions from Google after winning a battle with the Justice Department's antitrust division over which regulator would probe the world's most popular search engine. The complaints about skewed search results represent a far greater threat to Google's business than any of the FTC's other concerns, said Keith Hylton, a Boston University law professor who has written several books on antitrust topics.