US download music sales increased by 77% in the first half of 2006, while album sales fell by 4.2%, according to research company Nielsen Soundscan.
James Blunt topped the US singles chart earlier this year
More than 14 million full-album downloads were bought, compared with 6.5 million purchased during the first six months of 2005.
Top-selling albums of the year so far included those by Mary J Blige, James Blunt and Carrie Underwood.
Country music enjoyed a 17.7% increase in sales.
The decline in album sales has been partly attributed to a dearth of big hits so far this year - in contrast, Mariah Carey and 50 Cent both released multi-platinum albums in the early part of 2005.
"Considering that you haven't had a 50 Cent to be the Pied Piper during the first half of the year or a Norah Jones the year before that, being behind 4% in album sales is really not that bad," said Geoff Mayfield, director of charts for music magazine Billboard.
Although digital sales are growing, music fans are eschewing the more profitable full-album downloads in favour of cherry-picking a few songs.
"Digital distribution is an answer to the consumer who's been throwing up that complaint," Mr Mayfield said.
"It's a changing dynamic that the industry still needs to get its arms around."