Amazon recently announced the Fire phone, and the Seattle company is not stopping there. Its newest venture is Kindle Unlimited, an e-book and audiobook rental service. It launched on Friday, July 18, with a free 30-day trial and will run $9.99 a month for customers who want to subscribe to access the 600,000 e-book titles it carries.

Kindle Unlimited joins Scribd and Oyster in the growing digital book subscription marketplace. Scribd, which heavily advertises on Facebook, runs $8.99 per month for access to 400,000 books, while Oyster carries 500,000 and costs $9.95 per month.

The two companies have an advantage over Amazon because they carry titles from major publishers that are not making their offerings available through Kindle Unlimited.

According to reports, Amazon and Hachette have haggled over e-book prices, joining HarperCollins and Simon and Schuster on the sidelines. Penguin, Random House and Macmillan have not officially commented about their participation or lack thereof.

The U.S. e-book market grew 9 percent this year from 2013, with 79 million people consuming literature from e-book readers this year, according to a Mercury News report citing eMarketer. The market segment it most resonates with are adults age 45 to 54.

In addition to e-books, Kindle Unlimited also carries 2,000 audiobooks from Audible with Whispersync for Voice, which allows users to alternate between reading and listening to a book. Subscribers can test out Audible, which carries 150,000 titles, for three months for free.

According to the Mercury News report, the roll-out of Kindle Unlimited means Amazon is expanding beyond the Prime loyalty program, to which its video streaming set and grocery delivery service – as well as Fire smartphone – are connected. Kindle Unlimited is for wider use on Kindle devices or iOS or Android apps.