Album sales in the US are down 4.4% to 218.4 million units for the first nine months of the year, compared to the same period in 2011.
According to new Nielsen Soundscan figures, the drop has been fueled by CD sales dipping to 129.7 million units from 151.6 million units the year before.
The figures published by Billboard show that digital album sales are up 15.3% to 85.5 million units - not enough to make up the shortfall from declining CD sales.
Vinyl is also up, with a 16.3% increase to 3.2 million units from 2.7 million units in 2011 - around 1.5% of total US album sales this year.
Adele is the biggest-selling artist of the year so far, with four million units of 21 shifted in the the first nine months of 2012, bringing the LP's total sales to 9.85 million units.
A total of 1.009 billion digital tracks have been sold in the period - a 6% increase on the 951.7 million units posted in the first three quarters of 2011 combined.
Universal Music Group (UMG) was the top US album distributor with a market share of 29.83% in terms of albums plus track equivalents (TEA), just ahead of Sony by less than 1%. Sony Music posted 28.84%.
However, if only albums are taken into account Sony was the top distributor in the first nine months with 32% versus UMG's 26%.
In terms of pure track sales, UMG took a 31.2% track share - 6% ahead of Sony.