The new May online video rankings from comScore show that 176 million U.S Internet users, or about 83.3% of the U.S. Internet audience viewed online videos last month.
Users spent an average of 15.9 hours per viewer over the month. More than 5.6 billion viewing sessions were recorded that month, according to comScore.
Most of the viewing remained short, with the average duration only 5.2 minutes, while the length of average online video ad was 0.4 minutes.
Google sites, driven primarily by video viewing at YouTube.com, ranked as the top online video content property in May with 147.2 million unique viewers while viewers watched the most video ads at Hulu, which had 1.3 billion video ad impressions. Overall, Americans viewed 4.6 billion video ads in May.
Vevo was second-ranked company for video viewing, with 60.4 million unique viewers, followed by Yahoo! Sites with 55.5 million viewers, Facebook.com with 48.2 million viewers and fifth ranked Viacom Digital with 46.5 million viewers.
Other TV brands in the top 10 rankings of unique online video viewers included eighth-ranked Turner Digital with 35.2 million unique viewers; ninth-ranked NBCU with 30.6 million; and Hulu, which was 10th with 28.5 million.
Google Sites had the highest number of viewing sessions with more than 2.1 billion, and highest time spent per viewer at 311 minutes, crossing the 5-hour mark for the first time, comScore reported.
Americans viewed 4.6 billion video ads in May, about 12.6% of all videos viewed, and spent more than 2.0 billion minutes watching them, about 1.2 percent of all minutes spent viewing video online, with Hulu delivering the highest duration of video ads at 560 million minutes.
All told,, video ads reached 45%of the total U.S. population an average of 34 times during the month. Hulu also delivered the highest frequency of video ads to its viewers with an average of 48 over the course of the month.
After Hulu, which had 1.3 billion video ad impressions during the month, Tremor Media Video Network ranked second overall (and highest among video ad networks) with 700.8 million ad views, followed by Adap.tv (642 million) and BrightRoll Video Network (565 million), according to comScore.
Other TV brands in the top 10 included Viacom Digital at number seven (265.8 million impressions), eighth ranked CBS Interactive (258.8 million) and tenth ranked ABC Television (181.7 million).
The top video ad networks in terms of their potential reach of the total U.S. population were: Tremor Media at 47.1%, BrightRoll Video Network at 42.1% and Break Media at 40.4%, comScore found.