Around the time of Jackson's death, only one of his albums ranked in the top 100 on iTunes in the United States. By Friday morning, eight of the top 10 albums were Jackson's. An "Essential" collection of Jackson's songs compiled by Apple's iTunes music team was the top-selling album, followed by "Thriller."

Five of Jackson's singles made it to iTunes' list of most-purchased tracks — "Man in the Mirror," "Thriller," "The Way You Make Me Feel," "Don't Stop 'Til You Get Enough," and "Smooth Criminal" — in what may be one of the best barometers to gauge his most popular songs.

With Amazon sold out of Jackson CDs, Carr said many customers were buying Jackson's music in digital form. Sales of Jackson-related videos are also up on Amazon — Carr said most DVDs, including the 1978 movie musical "The Wiz," are currently out of stock.

Carr said it was difficult to say whether the increased sales would persist, saying Amazon for now was taking things "minute by minute" and reacting to customers' orders. "They love him, he's a legend, and they're anxious to make sure they have his music in their collections," he said.