That Adele's "21" will rank as the year's top-selling album is no surprise - the English singer-songwriter's hits "Rolling in the Deep" and "Someone Like You" dominated playlists in 2011. What is surprising is that "21," released by independent British label XL Recordings, sold more than 5 million copies.

The last time an album topped the year-end chart with more than 5 million copies sold was in 2004, when Usher's "Confessions" moved 7.9 million, according to Nielsen Soundscan, which supplied all sales data for this story.

Indeed, music sales overall are expected to end 2011 up more than 3 percent from last year. Not coincidentally, the last time overall music sales rose by so much was in 2004 as well.

The resurgence in sales is welcome news for the music industry. A meager 1 percent increase in digital sales last year created widespread panic that the format had already plateaued.

Nielsen analyst David Bakula attributed the rebound to a strong release slate, plus retailers getting more aggressive with pricing and promotions.

For instance, Lady Gaga's album "Born This Way" was priced at 99 cents - less than one-tenth the price of most albums - in a special deal, helping drive sales beyond her core fans, he said. The promotion on Amazon.com angered other retailers who were selling the album at full price, however.