Google, bolstered by YouTube, topped analytics firm ComScore’s list of the most-watched video sites on the Web.

The report, issued Friday, found that YouTube visitors spent more than five hours watching video on the site in May 2011. Google sites were followed by VEVO and Yahoo! sites. Facebook and Viacom Digital rounded out the top five.

And while Hulu was the last-place site in the top ten for unique viewers, it had the highest number of ad impressions of any site included in the survey.

The report also found that 83.3 percent of the U.S. online audience viewed online video last month and that ads accounted for 1.2 percent of all time spent viewing video online.