After months of speculation, Amazon on Friday introduced a digital subscription service that allows subscribers unlimited access to a library e-books and audiobooks for $10 a month.

The service, Kindle Unlimited, offers a Netflix-style, all-you-can-read approach to more than 600,000 e-books, including blockbuster series like "The Hunger Games" and "Diary of a Wimpy Kid," nonfiction titles like "Flash Boys" by Michael Lewis, as well as literary fiction and classics.

So far, however, none of the five biggest publishers appear to be making their books available through the service.

HarperCollins, Hachette and Simon & Schuster, for example, are not participating, representatives from the three companies confirmed.

Penguin Random House and Macmillan declined to comment, but a search on Amazon suggests that they are not making their books available. As a result, some popular titles were noticeably absent when the service began on Friday.

Among the imprints making their books available to the service are Scholastic, which published "The Hunger Games" series, and Houghton Mifflin Harcourt.

News of Kindle Unlimited was reported earlier this week, when Amazon accidentally posted a promotional video for the subscription model. The video was quickly taken down from Amazon’s website, but not before technology bloggers noticed.

In offering the service, Amazon is entering an increasingly crowded marketplace. It will be competing with publishing start-ups offering similar services, like Scribd and Oyster, which charge a comparable subscription fee and have comparable digital libraries.

Scribd has some 400,000 titles and charges subscribers $9 a month. Oyster has more than 500,000 titles available and gives readers unlimited access for $10 a month.

With similar pricing models, the competition among e-book subscription services could come down to content and what books and authors are included.

Scribd’s subscription service includes books from more than 900 publishers, including Simon & Schuster, HarperCollins and Wiley. Oyster offers titles from six of the top 10 American publishers, according to a company representative.

Publishers receive payments whenever one of their books is downloaded and a certain percentage is read.

Amazon is entering the arena with a huge advantage: its dominance within digital publishing, and its vast audiobook library, which it is bundling into the subscription service. Amazon owns Audible and is including more than 2,000 digital audio titles in Kindle Unlimited. Through the company’s Whispersync for Voice technology, users can toggle between digital audiobooks and e-books, alternately listening and reading without losing their place in the story.