Book of 99 is Relax Gaming’s take on the classic “Book of” slot format, built around Greek mythology and distinguished by an RTP of 99% — far above the roughly 96% average for the genre and, at launch, the highest RTP of any “Book of” style slot on the market. It plays on a 5×3 grid with 10 fixed paylines and high volatility, and adds a book-collection meter alongside the standard three-scatter trigger: land 99 book symbols over the course of base-game play and the free spins round fires automatically, even without hitting three scatters on a single spin.
Book of 99 isn’t available at either of our linked casinos — both are RTG-powered, and Relax Gaming, a regulated-market studio, doesn’t license its titles to RTG-style offshore casinos. Try Sloto Cash instead for a working real-money slots option, or play Book of 99 in demo mode at Relax Gaming’s own site if it’s listed there.
| Provider | Relax Gaming |
| RTP | 99% |
| Volatility | High |
| Reels / Rows | 5 / 3 |
| Paylines | 10 (fixed) |
| Max Win | 12,075× stake |
| Release Year | 2022 |
The book symbol in Book of 99 acts as both a wild and a scatter, and landing three or more anywhere on the reels triggers 10 free spins in the usual way — but the game also tracks every book landed across ordinary base-game spins toward a separate 99-book counter, giving free spins two independent routes to trigger instead of one. Once the bonus starts, one of four mythological characters is chosen at random and becomes an expanding symbol for the round, growing to fill an entire reel whenever it appears and driving the round’s biggest multipliers. The 99% RTP is the headline number, but it comes paired with a high-volatility profile, so the extra return is concentrated in the size of occasional wins rather than in more frequent small ones.
Pros
- 99% RTP is exceptionally high for the “Book of” genre, well above the roughly 96% category average
- Dual free-spins triggers (three scatters, or a slow-building 99-book counter) give two paths into the bonus
- Expanding-symbol free spins round can produce large multipliers when the right character is drawn
- Simple, familiar 5×3, 10-payline layout that “Book of” fans will recognize instantly
- High RTP makes it a natural pick for players prioritizing long-run return over raw ceiling size
Cons
- 12,075× max win is modest next to Relax Gaming’s bigger-ceiling originals like the Money Train series
- High volatility means the 99% RTP doesn’t translate into frequent visible wins session to session
- 10 fixed paylines is a narrow structure compared to Megaways or cluster-pay Relax titles
- The 99-book counter can take a very long time to fill without hitting three scatters directly
Frequently Asked Questions
What is the RTP of Book of 99?
Book of 99 carries a 99% RTP from Relax Gaming, among the highest of any “Book of” style slot on the market.
How do you trigger free spins in Book of 99?
Free spins trigger either by landing three or more book symbols on a single spin, or by collecting 99 book symbols cumulatively across base-game spins.
Where can I play Book of 99 for real money?
Book of 99 isn’t available at Sloto Cash or Fair Go, our two linked casinos, since Relax Gaming doesn’t license its titles to RTG-style offshore operators — try Sloto Cash instead for a working real-money slots option, or check Relax Gaming’s own site for a demo.