The European Commission has decided to probe Google Inc. after complaints by search service providers about unfavourable treatment of their services in Google's search results.

There were also allegations that Google meted out preferential placement of its own services to shut out competing services.

The probe follows complaints from Microsoft Corp.'s German unit, U.K. price-comparison site Foundem, and French site

This initiation of proceedings does not imply that the commission has proof of any infringements. It only signifies that the commission will conduct an in-depth investigation of the case as a matter of priority, the commission said.

The commission will investigate whether Google has abused a dominant market position in online search by allegedly lowering the ranking of unpaid search results of competing services, and by according preferential placement to the results of its own vertical search services.

Google's internet search engine provides for two types of results when people look for information. These are unpaid search results, which are sometimes also referred to as natural, organic or algorithmic search results, and third party advertisements shown at the top and at the right hand side of Google's search results page.

The commission will also look into allegations that Google lowered the 'Quality Score' for sponsored links of competing vertical search services. The Quality Score is one of the factors that determine the price paid to Google by advertisers, it said.

In addition, the commission will probe whether Google imposes exclusivity obligations on advertising partners, preventing them from placing certain types of competing ads on their web sites, with the aim of shutting out competing search tools.

In response, Google said it would work with the commission to address any concerns.