A mere 38 per cent of fans were willing to pay anything at all, while two-thirds of fans paid only the 45p handling charge, according to comScore.
The average amount that fans were willing to pay was £2.90, far lower than the cost of a CD or downloading an album from the Apple iTunes store.
During the first 29 days of September, 1.2 million people worldwide visited the In Rainbows site, and a significant percentage downloaded the album.
ComScore found that 38 per cent of global downloaders paid for the album, while the remaining 62 per cent chose to pay nothing.
The percentage downloading for free in the US was 60 per cent, only slightly lower than the rest of the world (62 per cent).
"I am surprised by the number of freeloaders," said Fred Wilson, managing partner of Union Square Ventures and music aficionado.
"The stories to date about the In Rainbows ‘pick your price' download offer have been much more optimistic...this shows pretty conclusively that the majority of music consumers feel that digital recorded music should be free and is not worth paying for.
"That's a large group that can't be ignored and its time to come up with new business models to serve the freeloader market."