Book of 99 Slot

Book of 99 Slot
Published Date · May 14, 2021 · Last Updated · Feb. 21, 2024
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Book of 99 Slot Review

Book of 99 Slot Overview

Another title to take on the ‘Book of’ moniker, Book of 99 is brought to you by the superstars at Relax Gaming! Ancient Greece is the destination on this occasion as it plays host to an epic battle between heroes and villains. Literature fans will enjoy the homage paid to Homer’s Odyssey, with some of the slot’s characters borrowed from the legendary poem. With bonus rounds, free spins, a whopping 99% RTP and a chance to win up to 12,075x your stake, there’s plenty of opportunities to make your own history and walk away with some big wins.

Book of 99 Slot Details











12,075 x

Software Provider

Relax Gaming



Design and Layout

5 Reel Slots


Free Spins

For a slot game centred around the number 99, Relax Gaming has done its utmost to dress it up to the nines! The game is gorgeous to look at, and we’re not just talking about those hero icons. The visuals are sleek and make the game more polished as a result. It’s not jam-packed with bonus features, but its Free Spins Bonus is fun to play, and the fact that it can be triggered in two different ways adds an extra element to the gameplay. Then of course we get to that 99% RTP. It’s incredibly rare to see an RTP so high in online slots, so that is definitely a major plus point of Book of 99. If Book of 100 ever gets made, then slot players everywhere may lose their collective minds. Overall, the game is easy to enjoy, and an ideal starting point for anyone who is looking to dive deeper into the world of slots.


Free Spins Bonus With Expanding Symbols

99% RTP

Amazing Graphics


High Volatility

Limited Bonus Features

How To Play Book of 99 Slot

Min Bet

Max Bet

Max Win




Book of 99 Free Spins
Unlocking free spins
Book of 99 bonus round win
Huge bonus round winnings
Book of 99 K symbol winning combination
Low-value symbols forming a win
Book of 99 rules
Book of 99 game rules

Book of 99 Basic Rules

  • Book of 99 is set on a 5x3 grid with 10 paylines
  • Winning combinations are formed by matching three (in some cases two) or more symbols on adjacent reels from left to right.
  • Only the highest-paying combination for each payline pays out
  • Wins on multiple paylines are added
  • The Book Wild symbol substitutes for all symbols aside from expanding symbols (which only occur during the Free Spins Bonus).

Book of 99 Slot Paytable & Symbols

2 Symbols
3 Symbols
4 Symbols
5 Symbols
book of 99 symbol 1
book of 99 symbol 2 woman
book of 99 symbol 3 ogre
book of 99 symbol 4 harpy
book of 99 symbol ace
book of 99 symbol king
book of 99 symbol queen
book of 99 symbol jack
book of 99 symbol 10
book of 99 symbol book
Book (Wild)

The lower value icons within the slot are represented by playing card symbols 10-A, which pay out up to 15x your stake for landing five on the reels.

For higher value symbols, the cat-like creature Lamia and the Cyclops are worth up to 75x your stake for five-of-a-kind, the female hero Pythia is worth up to 200x your stake, while the male hero Apollo is the game’s most valuable symbol - worth up to 500x your stake for landing five-of-a-kind. For these premium symbols, you only need to match two on adjacent reels to form a winning combination.

Book of 99 Slot Paylines

Book of 99 uses the tried and tested slot game format of five reels and three rows, giving you 10 paylines to play with. As you’d expect, winning combinations are formed by matching three (in some cases two) or more symbols on adjacent reels from left to right.

Book of 99 - Paylines
Every winning line in Book of 99

Book of 99 Slot Features

Book of 99 revolves around a classic Free Spins Bonus - but another element is added to this bonus round here with the inclusion of the potentially-lucrative Expanding Symbols.

book of 99 base game
Base game
book of 99 game features
Slot features summarised

Wild Symbols

The Book symbol pulls double duty as both the game’s Scatter and Wild - substituting for all regular symbols and playing a pivotal role in triggering a Free Spins Bonus.

Expanding Symbols

book of 99 two expanding symbols
Apollo as an Expanding Symbol
Book of 99 four expanding symbols
Expanding Symbols in the bonus round

During the Free Spins Bonus, one symbol is randomly chosen to be the special symbol for the round’s duration. If that symbol appears, it will expand and behave like a Wild symbol by paying out on all 10 paylines - in addition to any normal wins acquired.

Wins involving the expanding symbol don’t have to be connected, meaning expanding symbols on the first, third and fifth reel offer a winning combination every time during this bonus round.

The chosen expanding symbol also impacts the max win potential in the game. The Male Hero is the most valuable symbol in both modes. As an expanding symbol, he pays out 5,000x. In the base game, he pays out 1x, 10x, 100x or 500x, depending on how many you land.

Our Verdict: We like the Expanding Symbols feature. The animations for them are fun, and highlight how well-designed the slot is. They also boost your winnings substantially so what’s not to like?

Book of 99 Slot Bonus Features

Although it isn't absolutely loaded with bonus features, Book of 99 does have an extra round to get excited about.

Book of 99 free spins book
Entering the Free Spins Bonus
Book of 99 book wilds
Matching Book Wilds trigger free spins
Book of 99 free spins meter
Filling the Free Spins Meter triggers the bonus

Free Spins Bonus

There are two different ways to trigger Book of 99’s Free Spins Bonus. The standard way is to land three of the Book Wild symbols across the reels on the same spin. Doing this will award 10 free spins.

Collection Bonus Feature

A feature synonymous with all of Relax Gaming's 'Book of' titles, the other way to trigger free spins is by collecting the Book symbols as you play.

When your Collection Meter reaches 99, you will be awarded 10 free spins. If for example you’ve accumulated 50 Book symbols but you launch the free spins round by landing three wilds, you will keep the symbols you’ve already collected and can continue to build your tally.

When triggering the Free Spins Bonus via collection, the bet size used during the round will be the same as the bet size you were using when you filled the Collection Meter.

Our Verdict: The free spins are a great addition to this slot, which help to break up the base game nicely. The fact that the free spins can be accessed in multiple ways is a nice touch which adds an extra layer of excitement when you’re spinning.

Play Book of 99 Demo for Free

Try out the Book of 99 slot demo to play for free without staking real money. Treat online slots demos as your betting strategy simulator, allowing you to refine your techniques for lucrative outcomes. Use demos to try games from different providers before making a choice, ensuring you find the ones that resonate with your gaming style.

Book of 99 Slot RTP & Volatility


Variable RTP


Hit Frequency





The biggest selling point of Book of 99 is its return to player (RTP) percentage, which sits at an unbelievable 99%. We think there’s a chance this may have influenced the naming of the game. The average slot game has an RTP of 96%, so the figure for Book of 99 is nothing short of fantastic!

Despite the abnormally high RTP, Book of 99 is rated as a high-volatility slot game. This means that wins won’t be too frequent, but they could be quite lucrative when they land.

Our Verdict: The 99% RTP is a massive selling point for Book of 99. The RTP is so far ahead of what we would normally expect that it makes this slot stand out in a big way. It really helps to compensate for the minimal bonus features included in the game.

Book of 99 Slot Graphics & Audio

The slot's presentation is of a high standard, creating an immersive experience for players.


The Greek Mythology theme is woven through this slot, with large columns bordering the reels and a night-side mountain range providing the backdrop the way they did in ancient times.

Each character symbol has its own animation for when it's involved in a winning combination, which helps to give each character more personality. If you land two Book symbols within the first four reels, the lights dim and the remaining reels become shrouded in flames in anticipation of landing a third Book and triggering the Free Spins Bonus. This extra layer of drama helps keep you on the edge of your seat.

The game settings also give you the option to skip the slot's intro sequence the next time you log on to play.

Book of 99 bonus round win
Bonus round winnings
Book of 99 Wild symbol win
Wild Symbol forms a win
Book of 99 base game with wilds
Base game action
Book of 99 Audio Settings
Audio settings


The music provides a mysterious vibe, making for a more immersive gaming experience. A thumping drumbeat accompanies your spins, thrusting you right into the throws of a battle in Ancient Egypt. When the character symbols appear in winning combinations during the Free Spins Bonus, you’ll hear them make specific sounds while your winnings are being totalled. Within the game settings, you have the option to turn off the slot's music and sound effects if you prefer to play in silence.

Our Verdict: It was clear to us how much care and attention Relax Gaming put into how Book of 99 looks. The character symbols come to life with their animations, making you feel at times like you're playing a console game rather than a regular slot. The colours are crisp and vibrant, making for a highly engaging playing experience.

Book of 99 Slot on Mobile

Responsive: Relax Gaming has created Book of 99 with the latest HTML5 technology. This means you should have no worries about how the game will perform on smaller screens, as the game remains highly responsive.

App: Book of 99 is playable on all iOS and Android devices, and the game’s performance remains consistent regardless of which platform you play on. Desktop players have the ability to play the slot on their web browser of choice as it runs just as well on Google Chrome, Safari or Microsoft Edge.

Book of 99

Book of 99 FAQs

When was Book of 99 slot released?

4th May 2021.

Are there free spins in the Book of 99 slot?

Yes - the game’s Free Spins Bonus gives you 10 free spins when activated.

What’s the RTP for Book of 99 slot?


Can I play Book of 99 slot on mobile?

Yes - the game is available to play on all iOS and Android devices.


Tim Williams

Head of Content

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