Amazon may be testing a new unlimited subscription program for Kindle e-books for $9.99 per month. This would be a direct challenge to competitors Oyster and Scribd, which offer similar programs at $9.95 and $8.99 per month, respectively. 

As first reported by Gigaom, the pages on Amazon are no longer accessible, so not just anyone can sign up— yet. But when you can, you'd reportedly have access to more than 600,000 titles and thousands of audiobooks. The audiobooks would likely come from Audible, which is owned by the e-tailer. [Amazon Kindle Fire HDX vs. Google Nexus 7: Which Tablet Is Better?]

It's unclear how many, or which audiobooks or e-books would be available, but it's a safe bet that some would be Amazon self-published titles. Currently, Amazon Prime members, who pay $99 per year, get access to one free e-book per month through the Kindle Lending Library. And through a Gold membership with Audible, users earn a credit (generally good for one audiobook) each month for a fee of $14.95. Prime members also get access to free two-day shipping, as well as free streaming of movies and music. 

Oyster, which has been called the Netflix of e-books, offers unlimited access to the company's library of 500,000 titles. The app stores the last 10 books you've opened for offline reading, and works on Android, iOS, Nook and Kindle Fire tablets. Everyone gets a free 30-day trial of the service when first signing up. 

Scribd also works across Android, iOS and Kindle Fire tablets, and comes with a 30-day free trial. But the service itself is $1 cheaper per month. The available library of e-books is 400,000 titles strong from more than 900 publishers. Scribd also lets you save up to 20 titles for offline reading. 

We are reaching out to Amazon for comment and will update this post if there is more news to share. 

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This story was originally written for LAPTOP and was republished with permission here. Copyright 2014 LAPTOP, a TechMediaNetwork company.