Amazon doesn't say how many Fires it has sold, but says it captured 22 percent of U.S. tablet sales over nine months. That would make it the second-most popular tablet, after the iPad. Based on iPad sales reported by Apple, Fire sales can be estimated at around 5 million units.
Separately, ABI Research said Thursday that sales of dedicated e-readers, such as the black-and-white Kindles, peaked last year. It expects worldwide sales of e-readers at 11 million in 2012, down from 15 million in 2011.
The research firm expects tablets to outsell e-readers nine to one this year, despite costing four or five time as much. Still, e-readers won't go away completely, ABI analyst Joshua Flood said.
"We believe there will always be a niche market for the dedicated reading device for voracious readers, business travelers, and educational segments, particularly ones that are low-priced," Flood said.
Amazon could update the rest of its Kindle line at next week's event, too. The current models were launched a year ago. In the intervening time, competitor Barnes & Noble Inc. has launched a Nook e-reader with a built-in screen illuminator for reading in the dark.
Amazon was the main outlet for the Kindle Fire. However, Staples stores recently sold it for $179.