MOUNTAIN VIEW, California: Ten months on from its $1.65 billion (€1.22bn; £832.79m) acquisition of video-sharing phenomenom YouTube, search giant Google is set to recoup some of its massive investment.

Until now the immensely popular website has been ad-free, although no-one (save its more naive users) expected that to last. And on Tuesday Google finally unveiled its YouTube advertising model.

It takes the shape of a semitransparent ad at the bottom 20% of the video, appearing fifteen seconds in from the video's start and vanishing around 10 seconds later unless the viewer clicks on it.

Viewers also have the option to zap the ad from the outset if they wish. But if a viewer chooses to watch the ad, the main video pauses until the commercial has run its course.

Initially Google will sell the ads only on videos provided by select content partners, whose original videos include professionally produced clips as well as user-generated content. Partners earn a share of the ad revenue.

According to Nielsen/NetRatings NetView, YouTube is America's most popular online video site.

Data sourced from Wall Street Journal Online. additional content by WARC staff