e-Books sold on Amazon.com can only be read on that company's Kindle or on Kindle software for iPhones. Sony's move toward open formats resembles the industry move toward MP3 audio to counter the lock Apple had on music at the beginning of its online iTunes Store. At that time, music sold by iTunes could only be played on Apple's iPod. Now those files are playable on other devices.

Not Just 'One Store'

Sony also said it will drop its anti-copying software and adopt one from Adobe Systems. Steve Haber, head of Sony's digital reading unit, told The New York Times that people looking for e-books will "want to shop at all the stores, and not just be required to shop at one store."

Sony's move comes as the e-book market is heating up. The Association of American Publishers has reported that e-book sales in the U.S. increased 136 percent in June compared to a year ago, although the dollar amount -- $14 million -- is still small by the standards of other content sales.

Amazon is pushing its newest, recently released Kindle with a new focus on textbooks and the educational market. Sony has released two new e-reader devices, dropped its prices for new book releases, and is expected to offer an e-reader with wireless capabilities by the end of this year, matching that feature of the Kindle.

The potential big rock that could be thrown into this still-small pond is Apple's. The computer and consumer-devices company has been rumored to be planning the release by year's end of a tablet computer, which could be well suited to e-publishing, among other uses. The iPhone and iPod are already being used as e-readers, although the small screens limit that appeal.

'An Advantage for Lesser-Known Companies'

Ross Rubin, director of industry analysis for consumer technology at NPD Group, said the adoption of the ePub format could be a step toward "an open ecosystem of Kindles and other e-readers."

Such an ecosystem, he said, would certainly "be an advantage for lesser-known companies to produce inexpensive readers," especially for companies that can't afford to also put up their own online store.

One challenge that Kindle could be facing as it tries to move into the educational market, he said, is that purchases "may have to be approved by institutions, such as colleges, which may insist on open standards or multiple options."

Rubin also pointed out that various e-readers also do or will support the PDF format, which could also allow content to be played on devices from multiple vendors.