EU anti-trust authorities are from Thursday testing for a month changes to Google's search results meant to respond to competitors' complaints that the US online giant was giving unfair prominence to its own links and ads.
The 'market test' trial stems from a 2010 inquiry opened after several complaints from companies including the portal Ciao, owned by Microsoft, that Google was abusing its dominant market position to promote its own businesses.
If the measures are deemed adequate, the EU's executive body, the European Commission, could make them binding on the company.
But if they are not, then Google could be fined an amount reaching as high as 10 percent of its global revenues.
US regulators in January closed their own similar probe into Google's practices by saying there was not enough evidence to prove the Internet giant was manipulating its search results to harm competitors.
Google controls around 70 percent of the online search market in the United States and around 90 percent in Europe.
In response to the EU probe, Google has committed itself to several remedies over the next five years, including clearly labelling search results that link to Google businesses, such as restaurant finders, and to put three competitors' links close by on the same page.
Google would also scrap exclusivity clauses with advertisers whose links pop up in relation to a search query.
Crucially, Google would also provide newspaper publishers with a mechanism to control the "display of their content in Google News," the Commission said
Competitors have a month in which to make their remarks on the changed practices.
EU Competition Commissioner Joaquin Almunia has said several times in recent months that he wanted to see the issue solved through an agreement with Google.
Almunia's spokesman, Antoine Colombani, Thursday told reporters that the European Commission would like to see the inquiry closed "after the summer vacation in the best-case scenario".
A Google spokesman in Brussels declined AFP's request for a comment, and said only that "we continue to work cooperatively with the European Commission."
Google's competitors and some consumer groups said the test period and proposed remedies were insufficient.
Thomas Vinje, a spokesman for FairSearch Europe, which groups smaller online search and technology businesses including Microsoft and the travel sites Expedia and TripAdvisor, said: "Google's proposed commitments appear to fall short of ending the preferential treatment at the heart of the Commission's case based on formal complaints from 17 companies."
BEUC, a European consumer group, said in a statement that its "initial reaction is one of disappointment as we do not think today's (Thursday's) proposals can credibly achieve these targets" of ensuring fair practices.
Six European countries, including France and Britain, have also launched joint action against Google to get it to scale back new monitoring powers that watchdogs believe violate EU privacy protection rules.