Google managed to avoid antitrust charges in the United States, where it has two-thirds market share, after a two-year investigation of similar issues. Google has faced a more hard-line approach in Europe, where critics have accused the antitrust authorities of relying too much on outside complaints from competitors rather than on evidence of consumer harm. That is somewhat of a sore point for European officials, who insist they share the same goals as the Americans when it comes to consumers.

In April, Google proposed to change its search results to clearly label results from some of its own properties, like Google Plus Local, and in some cases to show links from rival search engines. It also proposed giving competitors more control over how it used information from their sites in its vertical search results and making it easier for small businesses to transport their ad campaigns to other search engines.

The proposal was the first time Google had agreed to legally binding changes to its search results, and went much further than the minor concessions it made to the Federal Trade Commission in its inquiry.

Still, the proposal would not have required Google to change the algorithm that produces its search results. Also, if it had been accepted, Google would have escaped a possible fine of about 10 percent of its annual global revenue of about $50 billion and a formal finding of wrongdoing that could limit its ability to expand in Europe.

That was not enough for Google’s competitors, they told the commission during market testing. In May, as Mr. Almunia came under increasing pressure to give Google a tougher punishment, he hinted that it would need to improve its proposals.

The main complaint issued by rivals was that the most prominent changes, labeling Google’s own services and showing links to rivals, would have had minimal effect on traffic to competitors and would continue to favor Google properties. Google could use prime placement and rich graphics to attract viewers to Google products, and the problem would be worse on mobile devices, competitors told the commission.