SAN FRANCISCO (Reuters) – YouTube, which has had to pull copyrighted videos off its site after legal attacks by some big media franchises, has enjoyed a surge in U.S. audience share that leaves it far larger than the next 64 video-sharing sites combined, a survey found.

The U.S. market share of visits to YouTube, which Google Inc. (GOOG.O: Quote, Profile, Research) bought for $1.65 billion last November, rose 70 percent from January through May, online audience measurement firm Hitwise Inc. said in the survey published on Wednesday.

By contrast, visits to the next 64 largest sites tracked by Hitwise rose only 8 percent during 2007′s first five months.

“As of May 2007, YouTube’s market share was 50 percent greater than those 64 sites combined,” Hitwise research director LeeAnn Prescott said in a summary of her firm’s data.

YouTube’s share of the U.S. online video market was 60.2 percent in May, according to Hitwise. Its closest rival, News Corp.’s (NWSa.N: Quote, Profile, Research) MySpace Videos site, had 16.08 percent of market share, the survey of Web surfing habits showed.

YouTube’s sister site, Google Video, held 7.81 percent, while Yahoo Inc. (YHOO.O: Quote, Profile, Research) had 2.77 percent and Microsoft Corp.’s (MSFT.O: Quote, Profile, Research) MSN, 2.09 percent, according to the study.

Start-up Metacafe ranked No. 8 in U.S. visitors to video sites with 1.07 percent, Time Warner’s AOL Media had 0.94 percent and Veoh was No. 10 at 0.86 percent, Hitwise said.

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