YouTube ad sales on videos are on the rise

YouTube is still Google's toughest sell to advertisers, but the video is selling ads against about 9% of its video views in the U.S., up from just 6% a year ago.

YouTube's director-product management said in an interview with Ad Age that the company is selling ads against "hundreds of millions of views" each month.

YouTube declined to comment on the exact rate at which it is selling ads and keeps the exact percentage a closely held secret.

A YouTube spokesman confirmed that the social site is placing ads on more videos than Fox Interactive Media, parent of MySpace and IGN Entertainment.

Fox Interactive ranks No. 2 by ComScore's measure, with 463 million views in February, or about 8.7% of YouTube's 5.3 billion views in the U.S.