Oyster, the book subscription service rather than the London Underground travel pass, has raised $14 million in investment in order to further expand its company and plans to become the go-to place to read digital literature.

The service offers access to more than 100,000 books and is available online and through an application for iPhone, iPad and iPod touch for a flat $9.95 monthly subscription. It's a similar idea to that offered by Spotify for music and Netflix for movies and TV shows.

The app learns your reading preferences and curates personalised reading lists. It also offers other ways to discover books through the Oyster team's own suggestions or integration with social networking features. You can see what your friends are reading or have stored in their libraries.

Oyster is available only in the US at present, and hopes to expand to other regions in time. But the additional funding received will be used to solidify its current business structure rather than help with rapid expansion. That will include apps for other platforms, most likely including Android.

"We really needed to grow the team, expand the product and expand to new platforms," co-founder Eric Stromberg told Forbes. "We need to be really good at product design, technology, marketing partnerships and really good at finance."

It's early days, but there's certainly a gap in the market for a Spotify for books.

Read Petite is another idea in the same vein, which is being headed by Tim Waterstone, founder of Waterstones bookshops. Rather than offer full novels however, the monthly subscription service will provide access to serialisations and short stories. It was announced last year but is yet to launch. You can read more about it at readpetite.com.

READ: Waterstones founder to launch Read Petite, Spotify-style online book service