The company seems focused on selling the deluxe Kindle DX, with its larger screen at 9.7 inches instead of six inches, and a price of $379. Both devices feature free 3G coverage to download some 630,000 commercial e-books as well as 1.8 million free public-domain titles.

Next Generation?

The depletion of the basic Kindle supply comes amid reports, unconfirmed by Amazon, that it is preparing an upgraded version.

"One of the possible reasons that Amazon's e-reader inventory has been moving briskly is in preparation for a third-generation Kindle device," said ABI Research mobile -devices analyst Jeff Orr. "A price cut on gen-2 readers could test the waters for a future tiered offering [of the lower-priced model]; different screen sizes or Wi-Fi-only, for example." No current Kindle models offer a Wi-Fi connection.

Amazon faces a crowded field of competitors, including Barnes & Noble's nook and Sony's Reader, as well as a range of tablet computers rushing to market to compete with Apple's popular iPad, which has far more functionality and offers access to Apple's growing library of e-books, currently at 75,000.

Apple says it has sold 3.27 million iPads in about three months since its debut, and analysts predict sales for 2010 may reach as high as 12 million. Amazon hasn't released sales figures for the Kindle.

iCompetitors?

But Orr said the devices are reaching different markets.

"Kindle and iPad do not compete any more than Kindle and iPhone compete," said Orr. "Avid book readers are choosing between a dedicated e-reader or sticking with books. Computer users that want a home companion device may opt for a media tablet such as iPad, but choosing a media tablet over an e-reader doesn't appear to be part of the consideration set for consumers."

Amazon is well-placed in the e-book hierarchy. On July 19, it announced that, for the first time, it had sold more e-book downloads than hardcovers, at a rate of 143 e-books for every 100 hardcover books during the second quarter. But in addition to top competitor Barnes & Noble, Borders Books, the nation's second-largest book retailer, recently launched an online store and its own reader, the Kobo.

"As competition in the e-reader device market heats up and Amazon's market share erodes -- since they once had nearly 100 percent to themselves -- their strategy also has to evolve," Orr said. "Sony's Reader line has three segments. Barnes & Noble is looking to add a second product to its offering."

"It is plausible that Amazon wants to remain a significant vendor as lower-priced devices make the technology accessible to a broader audience," he added. "The timing for a next-gen product is also good in advance of 2010 end-of-year holiday buying where most of the year's unit volume will be derived."