Book Of 99 Pros & Cons
Book of 99 delivers an insane RTP, but the high volatility means your bankroll needs to survive prolonged droughts. It's got a solid bonus system with two trigger methods, though the expanding symbol you get is random luck.
- 99% RTP beats almost every slot online
- 12,075x max win is above average
- Two ways to trigger free spins (scatter or collection)
- Works perfectly on mobile devices
- Flexible €0.10 - €100 betting range
- 5/5 high volatility = brutal dry spells
- Base game can feel repetitive and slow
- Expanding symbol is random - can get stuck with low-value symbols
- No bonus buy feature available
- Some casinos exclude it from bonus promotions due to high RTP
Book of 99 Slot Review – Is the 99% RTP Actually Worth It?
Book of 99 from Relax Gaming stands out for one huge reason - it's got a 99% RTP, which is basically unheard of in modern slots. Most games sit between 96% and 96.5%, so this is a massive jump. Here at SlotsGamblers, we tested this Greek mythology slot to see whether the insane RTP lives up to the hype or is just marketing smoke. The game packs high volatility (5/5 on Relax's scale) with a max win of 12,075x your stake. You get expanding symbols, free spins, and a unique collection feature where you gather 99 book symbols to trigger the bonus. The theme follows Homer's Odyssey with Greek heroes and monsters across 5 reels and 10 paylines.
Look, the RTP sounds impressive on paper, but here's the thing - the base game can be dry, and which expanding symbol you get will make or break your bonus round. It's perfect for grinding through wagering requirements, but casual players might find the high volatility brutal.
| Specification | Details |
|---|---|
| Developer | Relax Gaming |
| Release Date | 2021 |
| Reels X Rows | 5x3 |
| Paylines | 10 (Fixed) |
| RTP | 99.00% |
| Volatility Level | High (5/5) |
| Min Bet | €0.10 |
| Max Bet | €100 |
| Max Win Potential | 12,075x stake |
| Hit Frequency | 29.83% |
| Default Bet Range | €0.10 - €100 |
| Mobile Compatible | Yes |
Symbols & Payouts
The lower-paying symbols are typical poker ranks, with payouts ranging from 0.5x to 15x your stake. In contrast, the higher-paying symbols are various characters from Greek mythology that pay from 2-of-a-kind combinations and above. The wild symbol is the Book, and it substitutes for all other symbols except the special expanding symbol that appears during free spins, plus it serves as a scatter symbol that triggers the free spins.
🏛️ Apollo (Greek Hero) - High Value
The maximum win possible is 500x your bet for landing five Apollo symbols. This is your top-paying regular symbol, a warrior in golden armor. He appears more often than the other premium symbols. When he's chosen as the expanding symbol during free spins, you're in for the best possible bonus round. His design is sharp with nice detail on the armor and face. You want to see this guy as much as possible because five of them on a payline is your ticket to the max win potential.
👹 Polyphemus (Cyclops) - High Value
The one-eyed Cyclops is genuinely creepy-looking with a bulging eye and menacing grin. This character pays 250x for five of a kind, making it the second-best symbol. You'll encounter fearsome creatures like Polyphemus while navigating the classic Greek temple grid. The design has that cartoonish Relax Gaming style, but still manages to look intimidating. It pays from 2-of-a-kind, so you'll hit smaller wins with this symbol regularly. When it expands in the bonus, it can deliver solid payouts.
🧛 Lamia (Female Villain) - High Value
This symbol genuinely freaked me out when a winning combo landed! Lamia has a pale, haunting face, dark eyes, and sharp features. Five of these pay around 200x your bet. The character design is probably the most unsettling in the game, and it fits the Greek mythology theme perfectly. It's a medium-frequency symbol that'll appear regularly in both the base game and free spins—decent mid-tier value when you land multiple on a payline.
🔮 Pythia (Oracle) - Medium Value
The oracle appears as a mystical female figure in purple robes, paying around 150x for five of a kind. The design is less creepy than Lamia but still carries that mythical vibe. This symbol hits the balance between frequency and value, so you'll see it often enough to build your bankroll during base gameplay. You'll meet some of the most powerful Greek mythology-based characters, and Pythia is one of them. Animation is smooth when you land winning combos.
🃏 Ace (A) - Low Value
Playing card symbol styled with Greek temple patterns and golden edges. Five aces pay 15x your stake, so it's not huge, but they land constantly. The design fits the theme better than standard card symbols you see in other slots. These low-value symbols keep your balance from draining too fast during dry spells between bonus rounds. Expect to see a lot of these mixed in with the premium symbols.
🃏 King (K) - Low Value
Similar styling to the Ace with Greek decorative elements. Pays 10x for five of a kind. These show up so frequently that they'll be your primary source of small wins in the base game. The design is clean and fits the aesthetic without being overly distracting. When the bonus round picks a card symbol as the expanding one, it isn't enjoyable. However, it still pays on every line regardless of connection.
🃏 Queen (Q) - Low Value
Another card symbol with golden Greek borders, paying around 8x for five, super common appearance rate. You'll rack up tiny wins with Queens constantly. While it's not exciting, it prevents your balance from vanishing during long bonus hunts. The styling at least makes these card symbols feel integrated into the theme rather than slapped on as an afterthought, like some slots do.
📖 Book Symbol - Wild & Scatter
The book has golden covers with two shining red stones on the front. It is the primary trigger for Free Spins and acts as a Wild, helping you create winning combinations. This symbol does triple duty by substituting for other symbols, filling the collection meter, and triggering free spins when you land 3+. The animation, when it lands, is a golden glow effect. Landing 3 or more wild symbols will award 10 free spins. Every single book that lands in the base game gets added to your collection meter on the side.
| Symbol | 5 of a Kind | 4 of a Kind | 3 of a Kind | 2 of a Kind | Special Properties |
|---|---|---|---|---|---|
|
Apollo (Hero)
|
500x | 100x | 25x | 5x | Highest paying symbol |
|
Polyphemus (Cyclops)
|
250x | 50x | 15x | 3x | Second highest |
|
Lamia (Villain)
|
200x | 40x | 12x | 2x | Creepy design |
|
Pythia (Oracle)
|
150x | 30x | 10x | 2x | Medium value |
|
Ace (A)
|
15x | 5x | 2x | - | Most common |
|
King (K)
|
10x | 4x | 1.5x | - | Very common |
|
Queen (Q)
|
8x | 3x | 1x | - | Very common |
|
Book
|
Wild + Scatter | Wild + Scatter | Triggers Bonus | - | Collects to meter, substitutes all |
Bonus Features
The gameplay is straightforward, with only Free Spins and a theme that many online slots have used. There are no other features besides the Free Spins, but the book collection caught our eye. Two trigger methods give you more frequent access to the main bonus than standard book slots do.
| Feature Name | Trigger Method | Description | Max Potential Win | Frequency | Re-trigger Possible |
|---|---|---|---|---|---|
|
Free Spins (Standard)
|
3+ Book Scatters | 10 free spins with 1 random expanding symbol | 12,075x | Medium | Yes (3+ books) |
|
Collection Free Spins
|
Collect 99 Books | 10 free spins at average bet from collection period | 12,075x | Rare (300-400 base spins) | Yes (3+ books) |
|
Expanding Symbol
|
Automatically during Free Spins | One symbol expands to fill reels, pays on all lines | Depends on symbol | Every Free Spins round | N/A |
|
Wild Symbol
|
Random in base game | Book substitutes for all symbols, collects to meter | N/A | Common | N/A |
RTP & Volatility
The record-breaking 99% RTP is undoubtedly the big headliner. Few games are even close to such numbers—high volatility, scoring 5 out of 5 on Relax Gaming's own volatility scale. Max win is 12,075x your stake, which is above average even for this volatility level.
| Stat | Value |
|---|---|
|
Min Bet
|
€0.10 |
|
Max Bet
|
€100 |
|
Max Win (at min bet)
|
€1,207.50 |
|
Max Win (at max bet)
|
€1,207,500 |
|
RTP %
|
99.00% |
|
Volatility
|
High (5/5) |
Mobile
Relax Gaming is famous amongst players for its mobile slots, and Book of 99 does not disappoint in that regard. The bold, yet simple graphics translate great onto smaller screens. The user interface has been adapted from the desktop version to ensure easy navigation and smooth playability. It ran without a glitch when tested on an iPhone 13 mini. All the features and animations looked just as good on a much smaller screen. The Wild collection map moves up above the reels in portrait mode. It made playing the slot easy with just one hand, and it seems very well thought out for mobile casino fans. Works perfectly on Android and iOS devices, whether through a browser or casino apps.
Tips & Strategy
Grind the collection meter at low bets
Since collection free spins use your average bet during the collecting period, smart players bet a minimum €0.10 during the 300-400 spins needed, then can increase bet before manually triggering other bonuses.
Bankroll for 300+ spins minimum
Collecting 99 book symbols typically takes between 300-400 spins, so budget accordingly if you're chasing the collection bonus.
Perfect for wagering requirements
Here at SlotsGamblers, we recommend this slot specifically for clearing bonus playthrough thanks to that 99% RTP and only 1% house edge.
Watch for casino restrictions
Check if Book of 99 is excluded from your bonus before claiming promotions, since many operators block it due to the high RTP.
Don't chase losses in short sessions
High volatility means short-term volatility can destroy you. That 99% RTP only kicks in after hundreds of thousands of spins.
Similar Games
Mega Joker (NetEnt)
The only other well-known slot out there featuring a 99% RTP. You have to play with the highest possible stake to benefit from such returns, and you can win up to 2,000x your stake in the Supermeter Mode.
Book of Dead (Play'n GO)
Still the king of Book slots, despite customizable RTP ranges. The math model is as finely tuned as a trimmed Ferrari, and expanding bonus round symbols can lead to payouts up to 5,000x your stake.
Book of Sun: Choice (Booongo)
The highest RTP alternative to Book of 99 with theoretical returns of 97.74% for the Bonus Buy option. It offers expanding symbols in the bonus round and payouts up to 5,000x your stake.
Legacy of Dead (Play'n GO)
Another Greek mythology book slot with similar expanding symbol mechanics but lower RTP around 96%. Good if you want the same style with less volatility.
Play Responsibly - 18+ Only
Gambling should be entertaining and fun. Remember that slots are games of chance, and there's no guaranteed way to win. Never gamble more than you can afford to lose, and always set limits for yourself. If you feel gambling is becoming a problem, please seek help immediately.
FAQ - Frequently Asked Questions
Is the 99% RTP actually legit, or is it marketing BS?
The 99% RTP is among the highest theoretical returns you'll find, and it's significantly above the industry average of 95-96%. The game comes with an exceptionally high RTP of 99%. It's completely legit, but remember it only applies over hundreds of thousands of spins. Short sessions can still drain your bankroll fast.
How long does it actually take to collect 99 books?
Collecting 99 book scatters typically takes between 300-400 spins on average. We tested this at SlotsGamblers and hit the collection trigger after about 350 spins, betting €0.20 per spin. Budget your bankroll for at least 300+ spins.
Can I pick which symbol expands during free spins?
Nah, it's completely random. During free spins, a special expanding symbol is randomly selected before the round starts. You might get lucky with Apollo (best) or stuck with a low card symbol (worst)—no control over it.
What's the difference between the two ways to trigger free spins?
When you enter Free Spins by collecting 99 books, the slot counts the average bet you've placed throughout your gameplay. Therefore, instead of playing with your active stake, you'll receive another number that can be bigger or smaller. The standard 3-scatter trigger uses your current bet. Smart players bet low during collection periods.
Why do so many casinos exclude Book of 99 from bonuses?
Some casinos/slot sites will not allow this game to be part of a welcome offer or free spins promotion due to the return rate. Operators lose money on the 99% RTP, so they either exclude it completely or weigh it at 0% for wagering. Always check bonus terms.
Is Book of 99 better than Book of Dead?
Depends on what you want. Book of 99 has way higher RTP (99% vs 96.21%), but Book of Dead is still the king of Book slots with a math model as finely tuned as a trimmed Ferrari. Book of Dead is more balanced and entertaining, while Book of 99 is better for bonus grinding.
What's the best expanding symbol to get during free spins?
Apollo pays 500x your bet for landing five symbols. If all reels are filled with Apollo, the 500x win occurs on all 10 paylines, giving a 5,000x bet payout. That's your best-case scenario. Second best is Polyphemus at 250x per line. The worst is getting a low card symbol.
Can the free spins retrigger multiple times?
Yeah, no matter how you trigger the free spins bonus, it can be retriggered by landing three more scatters. You'll get 10 more free spins each time you retrigger. Retriggers happen often, so you can chain together 20-30+ spins if you're lucky.