RESTON, VA: The typical US viewer watched 14.6 hours of online video in December 2010, with ads served to sites such as YouTube also increasing their reach over the course of the month.
According to the new comScore figures, 172 million web users, 84.6% of the nation's total internet audience, watched some form of online video content. In all, there were 5.2bn viewing sessions.
Both of these totals held broadly steady from November 2010.
But the number of online video ads viewed increased over the month, with 48.6% of the population reached by the communications in November and 49.1% in December.
Overall, 16.4% of total videos viewed were ads, and 1.6% of the time spent by viewers watching video was spent watching an ad.
Google sites, which include YouTube, maintained their stranglehold on the sector, beating rivals in both unique viewer numbers (144.7m in December), viewing sessions (1.9bn) and minutes watched per viewer (873.1, or eight and a half hours).
Google's nearest rival in viewing sessions was music video network VEVO, on 266m, while Yahoo! video sites came closest for unique viewers on 53m.
The narrowest margin of victory for Google came for minutes watched per viewer.
Hulu, a website on which viewers can re-watch on demand various TV shows, had a per-viewer average of 217.1 minutes.
But Google was beaten for video ad impressions by several other sites, suggesting that the firm's sites have yet to be monetised as efficiently as those of its rivals.
YouTube has introduced many different types of ads to the site - including pop-ups, pre-rolls and traditional banners - over recent months in an attempt to boost its revenues.
But TV show-based services are able to include a higher ratio of ads to videos.
While Hulu topped the charts for December on 1.2bn video ad impressions, Google trailed in ninth place with just over 220m impressions, and was beaten out by video sites from firms including AOL, CBS and Microsoft.
Speaking to the OMMA video conference earlier this week, comScore analyst Dan Piech suggested that more ad dollars will migrate to online video over the years to come.
GigaOM reports Piech as predicting that the amount generated by the ads will rise to $5.2bn (€3.8bn, £3.3bn) in 2015 from $1.4bn in 2010.
Data sourced from comScore/GigaOM; additional content by Warc staff