Oyster, which has been described as the "Netflix for e-books" with its unlimited monthly subscription plan, said the agreements will mean "virtually any book" from the major publishers will be available for instant purchase.
The subscription service offers unlimited access to some one million books, but the most recent and popular titles have been excluded. The new e-bookstore will allow consumers to purchase those titles individually.
"We are expanding Oyster so you can access all your options -- subscription and for-purchase -- in one place," Oyster said on its blog.
For the new online store, Oyster will include titles from Hachette, HarperCollins, Macmillan, Penguin Random House, Simon & Schuster, and others, according to a statement.
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With the new publishing deals, Oyster will vastly boost the amount of content available on its website.
Still, it faces competition from Amazon -- which also offers a similar subscription service -- and from other digital book providers including Apple, Google and Barnes & Noble.