The U.S. Federal Trade Commission will not try to block Google's acquisition of online ad-serving vendor DoubleClick, the agency said Thursday.

The commission voted 4-1 to approve the deal after an eight-month investigation. "After carefully reviewing the evidence, we have concluded that Google's proposed acquisition of DoubleClick is unlikely to substantially lessen competition," the majority wrote in a statement.

The commission downplayed concerns brought by some privacy groups. Privacy concerns are "not unique to Google and DoubleClick," and "extend to the entire online advertising marketplace," commissioners wrote.

Google, the provider of the most widely used search engine, announced in April that it planned to acquire ad serving giant DoubleClick in a $3.1 billion deal.

The commission examined several factors and concluded that the two companies are not direct competitors, the FTC said in a news release on Thursday. The agency found that competition in online ad-serving markets is vigorous and likely to increase.

The agency will closely monitor the ad-serving space, however, commissioners wrote. "The markets within the online advertising space continue to quickly evolve, and predicting their future course is not a simple task," the majority wrote. "We want to be clear ... that we will closely watch these markets and, should Google engage in unlawful tying or other anticompetitive conduct, the commission intends to act quickly."

Google, which faces a similar examination before the European Union, praised the FTC decision.

"The FTC's strong support sends a clear message: this acquisition poses no risk to competition and will benefit consumers," Eric Schmidt, Google's chairman and CEO, said in a statement. "We hope that the European Commission will soon reach the same conclusion, and we are confident that this deal will deliver more relevant ads for consumers, more choices for advertisers, and more opportunities for Web site publishers."

Google will remain committed to user privacy, Schmidt added. "For us, privacy does not begin or end with our purchase of DoubleClick," he said. "We have been protecting our users' privacy since our inception, and will continue to innovate in how we safeguard their information and maintain their trust."

The same month that Google and DoubleClick announced the deal, three privacy groups, the Electronic Privacy Information Center, the Center for Digital Democracy (CDD), and the U.S. Public Interest Research Group (US PIRG), filed a petition asking the FTC to block the deal unless Google made significant changes to its privacy policy. The groups argued that the combined company with have unparalleled access to Web users' personal information.

The groups may look into filing a legal challenge to the deal, said Jeffrey Chester, CDD's executive director.

"The Federal Trade Commission sidestepped its responsibility today when it approved the merger of two companies whose new, extended data-collection reach will give it unprecedented access to track our every move throughout the digital landscape," Chester said in an e-mail. "By permitting Google to combine the personal details, gleaned from our searches online and YouTube downloads, with the vast repository of information collected by DoubleClick, the FTC has sanctioned the creation of a new digital data colossus."

It's the FTC mission to protect privacy, Chester added. "Despite the FTC's claims, privacy is most certainly an antitrust issue," he said. "A key component of the online market dominance that companies such as Google have achieved is the aggregation and analysis of consumer profiles, including the merger of far-flung data sets and vast data warehouses that only a handful of companies now have at their disposal."