Microsoft entered the top four US providers of online video content during September, according to new comScore data.
The company's sites attracted 45.5 million unique viewers during the month, moving it up three places in the rankings.
Google remained the top provider of online video, attracting 144.2 million individual viewers mainly thanks to its YouTube site.
Yahoo! was second with 54.4 million unique viewers, while social network Facebook took third spot with 52.2 million.
Looking at online marketing services, comScore said Americans watched 4.3 billion video ads on the web last month.
Hulu, which offers TV shows over the internet, delivered the most ad impressions at 794 million.
It was followed by the Tremor Media Video Network and the BrightRoll Video Network, which recorded 526 million and 476 million views respectively.
In related news, a recent study by the UK's Internet Advertising Bureau and broadcaster Sky found that only six per cent of people who watch an online video click through immediately – but another 54 per cent acted on the information at a later date.
News brought to you by ClickThrough – experts in Search Engine Marketing & Internet Marketing.