Apple says that downloads of OS X Mountain Lion have exceeded three million in four days, making it the most successful OS X release in Apple’s history.

Mountain Lion is the ninth major release of Mac OS X. It’s available through the Mac App Store™ as an upgrade to Lion or Snow Leopard users for US$19.99 .

“Just a year after the incredibly successful introduction of Lion, customers have downloaded Mountain Lion over three million times in just four days, making it our most successful release ever,” says Philip Schiller, Apple’s senior vice president of Worldwide Marketing.