"This was truly the year of the billionaire bad boy in romance," said Sara Nelson, editorial director of books and Kindle at Amazon.com.
"While E.L. James published the first two books in her Fifty Shades trilogy in 2011, so they aren't eligible for our 2012 list, the series really took off this year and propelled the third installment and the omnibus edition onto our Top 10 list," she added in a statement.
Sylvia Day's "Bared to You: A Crossfire Novel" came in at No.4 and "No Easy Day: The Firsthand Account of the Mission That Killed Osama Bin Laden" by Mark Owen was fifth.
Day had two novels in Amazon's Top 10: "Reflected in You: A Crossfire Novel" captured the seventh spot, just ahead of John Grisham's "The Racketeer" and William Landay's "Defending Jacob: A Novel."
"The Marriage Bargain (Marriage to a Billionaire)" by Jennifer Probst was No. 6 and David Baldacci's "The Innocent" rounded out the Top 10.
(Reporting by Patricia Reaney; Editing by Christine Kearney and Jan Paschal)