Ads on several websites using DoubleClick went blank or entire websites failed to load, starting at around 9:40 a.m. ET (1440 GMT), according to a report on tech blog The Next Web.
Sites affected by the outage include the Wall Street Journal, Forbes.com and BBC.com.
"Our team has worked quickly to fix the software bug and DFP (DoubleClick for Publishers) is now back up and running, so our publisher partners can return to funding their content," a Google spokeswoman wrote in an email to Reuters.
The outage hit websites around the world across video, display and mobile formats.
Gannett Co Inc, publisher of USA Today, tweeted: "Enjoy your ad-free experience on http://usatoday.com right now, brought to you by Google!"
Founded in 1996, DoubleClick runs a digital marketplace that connects ad agencies, marketers and website publishers. Google acquired DoubleClick in 2007.
Google shares were marginally down Wednesday morning on the Nasdaq.
© Thomson Reuters 2014
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