Adele sold 4.4m copies of the album in 2012 after selling 5.8m in 2011. She crossed the 10m threshold in November and was only rivalled by Taylor Swift, whose Red was second on the list.
If her album sales continue apace in 2013, 21 will move into the top 10 list for sales since 1993, when SoundScan began current tracking methods.
Gotye scored the year's top-selling song with Somebody That I Used To Know featuring Kimbra. The song was downloaded a record 6.8m times. Carly Rae Jepsen's Call Me Maybe was next at 6.5m. Both songs are the first to cross the 6m digital sales mark, while fun. came close with 5.9m downloads of We Are Young, featuring Janelle Monae.
Forty one songs crossed the 2m download mark, helping drive digital and overall sales to a new high even as album sales began to drop again after a momentary gain.
A record 1.65bn music units -- combining physical albums, digital albums and digital songs -- were sold in 2012, fuelled by an increase of 9.1pc in total digital sales and a 14.1pc increase in digital album sales.
Overall, however, album sales declined 4.4pc. That continues a downward trend since 2004 that was only briefly halted by last year's 3pc gain -- mostly due to the surprise success of 21.
Only two genres showed album sales gains in 2012. Rock gained by 2pc and country, fuelled by the format's assault on the top 10, jumped 4.2 pc.
Swift led a record five country artists into the top 10, selling 3.1m copies of Red in just over two months.
Other country artists on the list included Carrie Underwood's Blown Away at No. 7 (1.2m) followed by Luke Bryan's Tailgates & Tanlines (1.1m) and Lionel Richie's duets album Tuskegee (1m).
One Direction nearly matched Swift's sales total, but did it with two songs -- Up All Night at No. 3 with 1.6m sold and Take Me Home fifth with 1.3m.