Almost three-quarters of US internet users watched an average of 158 minutes of online video during May, new research reveals.

The comScore Video Metrix report for May found that Google sites topped the monthly rankings with the highest number of unique video streamers and the most videos streamed.

Americans viewed more than 8.3 billion video streams online during May, and Google sites recorded 1.8 billion videos streamed (21.5 per cent share), 1.7 billion of which occurred at YouTube.

Fox Interactive Media ranked second with 680 million streams (8.1 per cent), followed by Yahoo sites with 387 million (4.6 per cent) and Viacom Digital with 237 million (2.8 per cent).

Nearly 132 million Americans viewed online streaming video in May. Google captured the largest streaming video audience with more than 64.9 million unique streamers, followed by Fox with 52.7 million and Yahoo with 35 million.

The average video stream duration was 2.5 minutes, according to the comScore Video Metrix report.