Book of 99 Slot Review

Battle the mighty Cyclops in the Book of 99 slot, an ancient Greek adventure from Relax Gaming.  It’s a superbly designed 5 reel, 10 payline game that comes with a free spins round where an expanding symbol fills the reel whenever it hits. This special symbol doesn’t have to appear on adjoining reels to trigger a win either. So far, so standard. What makes Book of 99 stand out is its massive 99% RTP rate. Find out more about this potentially game-changing slot in our fill Book of 99 review.

Where to Play Book of 99 Slot

LeoVegas Casino
  • 50 Wager-Free Spins
  • £100 in Bonuses
  • 2,650+ Slots
T&C Apply

New players only. No deposit needed. 3 days to claim & 3 day expiry. 10x free spins worth 10p on Book of Dead. Opt in & deposit £10, £25 or £50 within 7 days & further 7 days to wager cash stakes 35x to unlock reward (£50 on 2 deposits). 3 day exp. Wagering/game contributions vary. 25 wager-Free Spins x10p to added to Starburst with each qualifying deposit, 3 day expiry. 18+ #ad

Mr Green Casino
  • 50 Free Spins
  • PayPal Deposits/Cashouts
  • 2,000+ Slots
T&C Apply

18+. Play Safe. New UK customers only. Opt in required. 1x per customer. Free spins on Lucky Mr Green only Max. 50 free spins at £0.10/spin with 35x wagering. Spins expire 72 hours from issue. Game, country, currency, player restrictions and terms apply #ad

SlotsMillion Casino
  • 100% up to £20
  • 100 Bonus Spins
  • 3,100+ Slots
T&C Apply

New customers only. Min deposit £10. Bonus win limitation: x10 the value of the bonus amount granted. 40 spins upon first deposit, with 2×30 spins 24 and 48 hours thereafter. Spins coin value: £0.01. Winnings from spins are bonus funds. 48x wagering required for any bonus funds; within 7 days for deposit bonus and 24h for winnings from spins. Max bet £3: game restrictions apply. Full Tx & Cs apply. 18+. – PLAY RESPONSIBLY #ad

Book of 99 Slot RTP, Details & Wager Limits

The Book of 99 slot is played on a classic 5 reel, 3 row machine with 10 active paylines. To create a winning combination, land 3, 4 or 5 matching symbols or wilds from left to right on 1 of those paylines, starting from reel 1. Things are slightly different with the expanding symbols in the bonus feature which we’ll look at below.

Stake levels in range from 10p to £100 per spin thus catering to all players and pockets. Use the + and – tabs below the reels to set your desired stake.

As impressive as the design and gameplay are, what really makes Book of 99 stand out is the return to player rate. The Book of 99 RTP is 99%. That’s the best number I’ve seen from any online slot and much higher than you’ll find from most slots which usually hover around the 96% mark. If the RTP rate is important to you, check out the slots with the highest RTP.

When it comes to variance, it’s high as you’d expect. The max win is 5,000 x your total stake per spin. The best opportunities of winning big come in the free spins due to the expanding symbol. There’s a 29.83% hit frequency rate so nearly a third of spins will give you a winning combination.

Theme – Audio & Design Features – head to ancient Greece and take on Cyclops


The Book of 99 slot has an ancient Greek theme. With terrific design, it features mythological characters such as the giant one-eyed Cyclopes.  The comic book visuals are complemented by a rather haunting backing track that adds to the air of mystery.

Set against a rustic, night-time backdrop, the reels here are set within marble columns. There you’ll find A to 10 symbols in precious metals and embedded with gemstones.  They’re joined by a quartet of higher value symbols. There’s Lamia (a female daemon), cyclopes (the one-eyed monster) and male and female characters. The male hero is the most rewarding symbol. Land 2, 3, 4 or 5 of these on a payline and you’ll win a payout equal to 1, 10, 100 or 500 x your total stake.

The book symbol serves a dual role. It’s a wild that substitutes for all the standard symbols (apart from the expanding symbol in the bonus round). Landing 3 of them on the same spin triggers the Free Spins feature.

Book of 99 is available to play on all devices including smartphones, tablets and computers. You’ll find the same classy design and simple gameplay in all versions. Most importantly, the 99% RTP is present and correct no matter what sort of devices you’re using.

Book of 99 Bonus Features

In the Book of 99 slot game, the gameplay is straightforward. Free spins with special expanding symbols are the main feature offering. Slightly unusually, there are 2 ways to trigger the free spins.

Free Spins feature


Land 3 or more wild symbols on the same spin to activate the Free Spins feature. Your reward here is 10 free spins. Before the free spins begin, 1 of the standard symbols is picked at random. This will be the special expanding symbol for the whole of the feature.

On each free spin, a standard payout consideration is made. If a special symbol lands, it expands to fill the whole of the reel. In addition to standard payline wins, the special expanding symbol can pay out on all 10 paylines depending on how the symbols fall.

Winning combinations made up of the expanding symbol don’t have to be connected either. For example, expanding symbols on reels 1, 3 and 5 would result in a winning combination being formed in the free spins. Now, your max win depends on which symbol becomes the special expanding symbol:

Symbol(s) Max Win (Full Screen)
Q, J or 10 100 x stake
A or K 150 x stake
Cyclopes or Lamia 750 x stake
Female Character 2,000 x stake
Male Character 5,000 x stake

Now, landing 3 or more wild symbols will result in a retrigger and another 10 free spins. Like slots with a similar bonus feature, there’s no limit to how many free spins you can play with.

Collection feature

There’s a second way to trigger the Free Spins feature. Each time a wild symbol lands, it’s collected in a meter to the left of the reels. This is called the Collection feature.

With each wild, you’ll progress along a treasure map. When you have amassed 99 wilds, you’ll trigger the free spins. These come with the expanding symbol just like in a standard trigger. When you’ve played out your 10 free spins, the meter resets and you’ll start collecting wilds once again on a quest to reach 99.

Book of 99 Review Summary – it’s all about the 99% RTP  

I’ve played plenty of slots that come with free spins and an expanding symbol. Such as Book of Dead (Play ‘n GO) and Book of Ra Deluxe (Novomatic). Whilst the design may not be top-notch, it has all the elements you’d expect from a ‘Book of’ game. It has the added Collection feature which gives you an extra way to get into the free spins.

However, what sets the Book of 99 slot apart is the 99% RTP rate. You won’t find a better figure than that anywhere. With its impressive sound and visuals and classic bonus feature, Book of 99 would be a perfectly playable slot if it had an average RTP rate.

With that number standing at 99%, it becomes well worth considering if you enjoy the ancient theme. The key to big wins is to get a high value special expanding symbol in the free spins. This could be the difference of 100 or 5,000 x stake payouts per free spin.

Whether this will nudge other slot developers into inching up their RTP rates remains to be seen. However, some slot sites may not include Book of 99 in the wagering for their welcome bonuses or free spins due to the high RTP rate. That remains to be seen.

Book of 99 FAQs

What is the Book of 99 RTP?

The Book of 99 RTP rate is 99%. Yes, you read that correctly, the return to player rate is an eye-popping 99%. You won’t find a better number than that anywhere.

What is the Book of 99 max win?

The biggest possible win from Book of 99 is 5,000 x your total stake. This can be achieved by filling the reels with the high value male character symbol. This becomes more probable in the free spins if it’s a special expanding symbol.

Are there any Book of 99 free spins?

Yes, the Free Spins feature is played by landing 3 wild books. With unlimited free spins up for grabs, you’ll benefit from a special expanding symbol which makes it easier to achieve the 5,000 x stake max win.

How does the Collection feature work?

Collect 99 wilds and you’ll trigger the free spins. Known as the Collection feature, it offers you another way to enter the all-important Free Spins feature with a special expanding symbol.

Is there a Book of 99 free play version?

Yes, you can play the Book of 99 demo here at This allows you to try this high RTP game on mobile, tablet and desktop devices.

Book of 99 Slot Information

  • Game:
    Book of 99
  • Provider:
    Relax Gaming
  • Type:
    Video Slot
  • Reels:
  • Paylines:
  • Stakes Range:
    10p to £100
  • Bonus Features:
    Yes (2)
  • Free Spins/Multiplier:
  • RTP %:
  • Max Win:
    5,000 x
Review by Chris Taylor

Review by Chris Taylor

Chris is a slots expert that has reviewed and played over 4,000 online slots. Having being in the iGaming industry for over 16 years, he knows how slots work, how bonus features are triggered and how the RTP and variance affect the gameplay.