Back in 1991, SoundScan began tracking album sales in the United States. Since then, Billboard says only one album has sold 16 million copies.
Metallica's self-titled album (usually called The Black Album) sold about 3,000 copies last week. That pushed the album's total sales to 16,002,000. The Black Album has battled Shania Twain's Come On Over for the title of best selling album of the SoundScan era. Metallica overtook Shania back in 2009. Those two albums are the only ones that have sold more than 15 million copies.
Despite being released in 1991, Metallica's Black Album is sitting at 144 on the Billboard 200. It's been on that chart for 307 weeks. That's also a record in the SoundScan era.
Overall, 22 releases have sold at least 10 million copies since 1991.