Music fans in the US are buying almost twice as many singles in digital form over the internet as they are on CDs from stores, according to a report.
Apple's iTunes is one of the popular legal download services
Some 7.7 million tracks were bought and downloaded since the end of June - compared with four million CD singles sold, Billboard magazine reported.
The figures show the success of new legitimate music download services.
But some say online and CD single sales cannot be compared because so few singles are now released on CD.
Record companies have cut CD single releases because of falling sales, but fans can choose from 500,000 songs for $0.99 (£0.60) each on some internet services.
Legitimate download sites, such as Apple's iTunes, the newly relaunched Napster and Musicmatch, are the most popular.
They are trying to tempt fans from unauthorised free download services like Kazaa and Morpheus, which have been blamed by the music industry for falling CD sales.
In the week ending 26 October, 857,000 songs were sold over the internet - compared to just 170,000 in record shops, Billboard said.
But the best-selling CD single is still outstripping the most popular download, the magazine reported.
The top CD single, I Can Only Imagine by MercyMe, sold 6,900 copies in one week, compared with 4,700 for the biggest online track, OutKast's Hey Ya!, according to Billboard.
The digital sales had a "symbolic significance" because they marked the music industry's move to digital operations, Sean Ryan, vice president of music at RealNetworks, said.
"Selling individual songs as an offline strategy wasn't working all that well, but online it can be a huge hit," he said.
EMI Music executive Phil Quartararo said he was happy with the trend but was not yet attributing too much significance to it.
"Any way we can drive a consumer to purchase music as opposed to taking music is a win for the industry," he said.
Official sales tracking body Nielsen SoundScan began tracking download sales in the last week of June.