The European Union concluded its investigation into how the $3.1 billion acquisition would impact competitiveness in the online advertising arena. EU had promised to wrap up its investigation into the deal by April 2, which it did. Its competition regulator, the European Commission, has ruled that the acquisition won't curb competition for online ads.

"The commission's in-depth market investigation found that Google and DoubleClick were not exerting major competitive constraints on each other's activities and could, therefore, not be considered as competitors," the commission said in the statement announcing the favorable decision.

"The elimination of DoubleClick as a potential competitor would not have an adverse impact on competition in the online intermediation advertising services market," the commission said.

This is a severe blow to Google's archrivals, Microsoft, Yahoo and Time Warner. They have lobbied against the deal but have failed to demonstrate that Google will be able to quasi-monopolize the advertising market if the purchase goes ahead.

The Federal Trade Commission, in a 4-to-1 vote, allowed in December Google's purchase of DoubleClick to go ahead. Thus the FTC's 8-month antitrust investigation came to an end. However, commissioner Pamela Jones Harbour dissented and wrote a 13-page explanation, which argued that the Google-DoubleClick deal will significantly transform the market.

A political controversy over deleted documents and conflicts of interest among online rights groups have drawn a lot of criticisms to the Google-DoubleClick deal. David Drummond, the senior vice president of corporate development and chief legal officer at Google has assured the U.S. Senate in September last year that privacy is a primary issue for the company as Google’s business depends on it.