American internet ad revenues for the first six months of the year set a record at nearly $10 billion US, representing a roughly 27 per cent increase over the first half of 2006, say figures released Friday.

Internet advertising revenue climbed to nearly $5.1 billion for the second quarter of 2007, rising above the $5 billion mark for the first time in a quarter, according to a PricewaterhouseCoopers report for the Interactive Advertising Bureau.

The top 50 websites raked in more than 90 per cent of reported revenues in the first half of 2007, while the top 10 sites accounted for 70 per cent, according to the study.

Search ads, led by Google, remained the most lucrative form of online advertising, representing 41 per cent of revenue in the first half of 2007.

"The torrid growth of interactive advertising revenue persists, and these results are really no surprise but very welcome news," bureau president Randall Rothenberg, said in a release.

"More and more marketers have embraced the reality that interactive is the fulcrum on which their brand strategies need to be based, and we expect robust growth to continue."

The dollar figures include online advertising revenues from websites, commercial online services, free e-mail providers and all other companies reporting "meaningful" online advertising revenues.