Book of 99 Review: The Highest RTP Slot for Irish Punters

Relax Gaming has truly shaken up the Irish online slot market with the release of Book of 99. In a world where most developers are slowly creeping their return-to-player percentages downwards, Relax Gaming decided to go in the opposite direction, offering a theoretical return that is almost unheard of in the industry. For the savvy punter in Dublin or Cork, the headline figure is impossible to ignore. This game isn't just another entry in the saturated "Book of" genre; it is a mathematical statement that provides one of the fairest environments for wagering EUR in 2026.

The game is themed around Greek mythology, moving away from the dusty Egyptian tombs we’ve seen a thousand times before. Instead, players are treated to a high-definition odyssey inspired by Homer's Odyssey, featuring legendary heroes, cyclops, and sirens. The visual style is hand-drawn and incredibly polished, fitting perfectly into the premium lobbies of Irish-licensed casinos like Paddy Power and LeoVegas. For many local players, the appeal lies in the combination of this high-end aesthetic and a collection mechanic that ensures your loyalty to the game is actually rewarded over time.

In the current Irish gambling landscape, where transparency and player value are increasingly under the microscope, Book of 99 stands out as a beacon of fairness. It is a staple at GRAI-licensed sites, offering a reliable and regulated experience that punters can trust. While the "Book of" mechanic is familiar to anyone who has had a flutter on classics like Book of Dead, the addition of the 99% RTP and the symbol collection meter turns it into a much more strategic experience. It’s a game that rewards the patient player who understands that in the long run, the house edge is practically non-existent here.

The cultural impact of Book of 99 among the Irish high-roller community has been significant since its launch. It is frequently discussed in local forums as the "grinder's slot" because of its specific math model. Unlike many flash-in-the-pan releases, Book of 99 has sustained its popularity because it respects the player's bankroll. Whether you’re playing on a desktop at home or using a mobile app while commuting, the sense of progression provided by the collection meter keeps the engagement levels high, making every spin feel like it’s contributing to a larger goal.

Book of 99 Specifications

To understand why this game is such a disruptor in the Irish market, we need to look at the technical foundation. Relax Gaming has built a robust engine that combines traditional 5x3 mechanics with a revolutionary reward system. The game feels every bit like a premium 2026 release, with smooth animations and a user interface that is incredibly intuitive for both new players and seasoned veterans of the Irish slot scene.

• Provider: Relax Gaming
• RTP: 99.00% (Market Leading)
• Volatility: High / Very High
• Max Win: 12,075x your stake (Cumulative)
• Max Win per Spin: 5,000x your stake
• Min/Max Bet: €0.10 - €100
• Reels/Rows: 5x3
• Paylines: 10 Fixed
• Bonus Features: Wild Collection Mechanic (99 Wilds), Free Spins, Special Expanding Symbols
• Mobile: Fully Optimized for IE 2026
• Currency: EUR (€)

The unique diamond-sharp focus on the 99% RTP is what defines the technical appeal of this title. While most slots operate with a house edge of 4% or more, Relax Gaming has slashed this to a mere 1%, which is closer to the margins found in professional Blackjack or Baccarat. This technical choice dictates everything about the game's performance, from the frequency of wins to the way the free spins are triggered. It is a bold move that has forced other providers to rethink their strategy for the Irish market.

The user interface is designed for 2026 standards, meaning it is incredibly lightweight and responsive on all devices. Whether you are navigating the bet selector or checking the paytable, the interactions are instantaneous. The "Book Meter" is prominently displayed, serving as a constant visual cue of your progress. This level of technical polish ensures that the player remains focused on the gameplay rather than fighting with the software. It is a masterclass in modern slot engineering that prioritises the user experience above all else.

RTP, Volatility & Mathematical Advantage

The 99.00% RTP is more than just a marketing gimmick; it is a fundamental shift in how slot math works. For every €100 wagered on Book of 99 by Irish players, the game is theoretically designed to return €99.00. This is the closest you can get to a "fair toss" in the world of online slots. However, it is vital to remember that this RTP is calculated over millions of spins. In a single session, the high volatility means you can still experience significant swings, both up and down, but the long-term outlook is far better than almost any other game in the lobby.

High volatility is the trade-off for such a high RTP and a large maximum win. In Book of 99, you might go through periods where the wins are sparse, as the math model is designed to pay out in larger, more concentrated bursts—primarily in the Free Spins round. Irish punters who are used to the "all or nothing" style of high-variance slots will feel right at home here. It’s a game that requires a bit of "staying power" and a solid bankroll strategy to ensure you can weather the dry spells and reach the bonus features.

The maximum win potential is capped at 12,075x your stake for the entire bonus feature, while a single spin can award up to 5,000x. On a 99% RTP machine, this feels much more attainable than on standard games. For a player wagering €1.00 per spin, the potential for a €5,000 single-spin payout is a very real possibility. At the maximum bet of €100, the top prize per spin reaches €500,000. While hitting the max win is a rare event, the high RTP ensures that the journey towards it is paved with more frequent mid-sized wins than you would find on a 94% or 95% RTP slot.

For the strategic Irish player, the mathematical advantage of Book of 99 cannot be overstated. When you combine the 1% house edge with the guaranteed free spins from the collection mechanic, you have a game that offers genuine value. Many players in the Republic use Book of 99 as their "main" slot because they know that their money is being treated fairly. It’s a grand choice for anyone who wants to maximise their playtime and give themselves the best theoretical chance of walking away with a profit in EUR in the long run.

The sheer stability of the 99% RTP over long sessions makes it a favourite for those who enjoy using betting systems. While no system can guarantee a win, the narrow house edge means your strategies have a better chance of sustaining your bankroll. This is why you see so many Dublin-based high rollers sticking to this title for their larger sessions. They understand that every fraction of a percentage point in RTP counts when you are wagering significant amounts of EUR. It is simply the most logical choice for the value-conscious gambler.

How to Play Book of 99

Getting started with Book of 99 is a straightforward process that will be familiar to anyone who has spent time in an Irish online casino. Your first step is to adjust your total stake in EUR. The betting range is quite wide, starting at just €0.10 and going up to €100 per spin. This makes the game accessible to everyone, from the casual player looking for a bit of fun to the high roller chasing a half-million Euro payout. Once your bet is set, simply hit the play button to begin your journey across the ancient Mediterranean.

The symbols in Book of 99 are beautifully crafted and represent various characters from Homer's Odyssey. The low-value symbols are the traditional 10, J, Q, K, and A, rendered in a sharp, Greek-inspired font. The high-value symbols include legendary characters like Lamia, a Cyclops, and the gods Pythia and Apollo. Landing five of the Apollo symbols on a payline results in the game's top base-game payout of 500x. The interface is clean and uncluttered, with your balance and win amounts clearly displayed in EUR at the bottom of the screen.

The most important symbol to watch for is the Golden Book. This symbol plays a dual role: it is both the Wild and the Scatter. As a Wild, it substitutes for all other symbols to help create winning lines. As a Scatter, landing three or more anywhere on the reels will trigger the Free Spins bonus. But there is a third, unique function for the Book in this game. Every time a Golden Book lands on the reels during the base game, it is added to the "Collection Meter" on the left side of the screen.

Navigating the game is easy on any device, thanks to the streamlined 2026 interface. The settings menu allows you to adjust the volume, toggle "Quick Spin" mode for faster gameplay, and find all the information on symbol values and paylines. For Irish players who like a more automated experience, the "Autoplay" feature is highly customisable, allowing you to set win and loss limits in EUR. This is especially useful in a high-volatility game like Book of 99, as it helps you stay within your budget while you work on filling up that 99-book collection meter.

If you are new to "Book of" slots, the most important thing to understand is that the base game is primarily about survival and collection. You are looking for those high-value character connections, but your real focus should be on the books. Each book that lands is a small victory, bringing you closer to the powerful bonus round. This dual-track objective—winning on lines while collecting for the bonus—is what makes every spin in the base game feel meaningful and exciting. It is a very rewarding loop for the patient player.

The Collection Mechanic

The collection mechanic is what truly separates Book of 99 from every other "Book" slot in the Irish market. On the left-hand side of the reels, you’ll see a meter that requires 99 Book symbols to be filled. Every time a Book symbol lands on the grid during the base game—regardless of whether it results in a win—it is collected and added to the tally. Once you reach 99 books, the Free Spins feature is triggered automatically. This provides a clear, visible path to the game’s main feature and ensures that your loyalty is rewarded.

This mechanic is a game-changer for Irish punters who feel frustrated by the randomness of traditional scatter triggers. In most slots, you could go 500 spins without seeing a bonus. In Book of 99, you are always making progress. Even a losing spin that contains a Book symbol is a step closer to the free spins. It adds a layer of strategy to the game; if you are at 90/99 books, you know that a bonus round is imminent, which might influence how you manage your EUR stakes for the remaining spins.

The average number of spins required to fill the meter is generally around 150 to 200, though this can vary based on luck. However, having a "guaranteed" trigger point is incredibly satisfying. It turns the game into a session-based adventure rather than a series of disconnected spins. Many players in the Republic prefer this system because it removes the "near-miss" frustration of landing only two scatters. In Book of 99, those two scatters are still valuable because they add two points to your collection meter.

It is important to note that the collection meter is tied to your specific bet level. If you change your stake from €1.00 to €2.00, you will start a new meter for that stake. However, your progress on the €1.00 meter is saved and will be there when you return to that bet level. This prevents players from gaming the system by collecting 98 books at a low stake and then switching to a high stake for the 99th book. It’s a fair and transparent system that encourages consistent play at a level that suits your budget.

For many, the collection meter acts as a psychological anchor. It gives you a reason to keep spinning even when the reels are being stubborn. You are not just gambling; you are working towards a goal. This sense of progression is a key part of the modern 2026 slot experience, and Book of 99 was one of the first to perfect it. It transforms the relationship between the player and the game from one of pure chance to one of earned rewards and persistence.

Free Spins & Expanding Symbols

The Free Spins feature is where the massive potential of Book of 99 is truly unleashed. You can enter this round in two ways: either by landing three or more Book symbols on a single spin or by completing the 99-book collection meter. Regardless of how you enter, you are awarded 10 free spins. Before the round begins, a random symbol from the paytable is chosen to be the "Special Expanding Symbol." This symbol will be your key to hitting the big wins during the bonus.

During the free spins, the chosen symbol will expand to cover all three positions on its reel if enough of them land to create a win. Crucially, these symbols do not need to be on adjacent reels to pay out; they just need to land anywhere on the 10 paylines. For example, if your expanding symbol is Apollo and you land one on reel 1, one on reel 3, and one on reel 5, they will all expand and pay out as a three-of-a-kind win across all 10 lines. If you are lucky enough to land an expanding symbol on all five reels, you will fill the entire screen.

A full screen of the highest-paying Apollo symbol results in a win of 5,000x your stake. At a €1.00 bet, that’s a €5,000 hit in a single spin. Even the lower-value card symbols can provide significant wins when they expand across all five reels. The tension during the free spins is incredible, as you wait for those symbols to land and the expansion animation to trigger. It’s the classic "Book of" thrill, but backed by that 99% RTP that makes the whole experience feel more rewarding for the Irish punter.

The Free Spins can also be retriggered by landing three more Book symbols during the round. This awards another 10 spins with the same expanding symbol. There is no limit to how many times you can retrigger the bonus, leading to some legendary sessions where the wins just keep stacking up. Because the Book symbol is also a Wild, it helps you form regular wins during the free spins as well. It’s a high-octane, high-reward feature that has made Book of 99 a legend in the Irish online casino community.

There is a specific kind of magic that happens when a high-value symbol is selected for the expansion. While the lower symbols pay out more often, the gods and heroes can turn a single spin into a massive EUR withdrawal. Seeing the reels glow as the expanding symbols take over is the visual highlight of the entire game. It is this moment that every player is chasing from the very first spin of the base game. Relax Gaming has truly mastered the art of the "big win" reveal.

Where to Play in Ireland

Finding a place to play Book of 99 is easy, as Relax Gaming is a top-tier provider supported by all the major Irish operators. However, because of the high RTP, you want to ensure you are playing at a site that offers fast EUR withdrawals and a secure environment. In 2026, the standard for Irish players is very high, and the following casinos are the best places to test your luck with this mythological masterpiece.

Paddy Power is an Irish institution and one of the most trusted names in the Republic. They have a fantastic relationship with Relax Gaming and often feature Book of 99 in their "Premium Slots" section. Playing here gives you the peace of mind that comes with a local, regulated brand. Their mobile app is second to none, and they are famous for their lightning-fast withdrawals to Irish bank accounts and Revolut. If you want a reliable and high-quality experience, Paddy Power is the place to be for a grand flutter.

LeoVegas is known as the "King of Mobile," and they certainly live up to that reputation when it comes to high RTP slots. Their platform is incredibly fast and intuitive, making it the perfect home for Book of 99. They offer a very generous welcome bonus for new Irish players, which can provide a significant boost to your bankroll as you start collecting those books. Their customer support is excellent, and they have won numerous awards for their commitment to a mobile-first gaming experience that is perfect for the modern punter.

Bet365 is a global powerhouse that has a massive following in Ireland. They are known for their professionalism, their vast library of games, and their exceptionally fast payout speeds. Book of 99 runs flawlessly on their site, and they offer a very clean, distraction-free environment for your gaming. They fully support Revolut for both deposits and withdrawals in EUR, making it incredibly easy to manage your funds. For the player who values efficiency and reliability, Bet365 is a top-tier choice for any session.

BoyleSports is another homegrown Irish favourite that treats its players right. They have a strong focus on the local market and offer a very secure and transparent platform for all types of gambling. Their selection of Relax Gaming slots is excellent, and they often run promotions that are tailored specifically for Irish punters. With full GRAI licensing and a reputation for fair play, BoyleSports is a grand option for anyone looking to have a flutter on Book of 99 in a safe and familiar environment with local support.

FAQ

Is Book of 99 the highest RTP slot in Ireland?

As of 2026, Book of 99 is indeed one of the highest RTP slots available to Irish players, sitting at a remarkable 99.00%. While a few other niche titles might come close, Book of 99 is the most popular and widely available game with such a high return percentage. This makes it a top choice for players who want to minimise the house edge while enjoying their session.

How many books do I need for the guaranteed bonus?

You need to collect exactly 99 Book symbols to fill the meter and trigger the guaranteed Free Spins round. Every Book that lands on the reels during the base game counts as one point towards this goal, providing a clear path to the game's main feature. This unique mechanic ensures that every spin is actually contributing to an eventual bonus trigger for the player.

Can I play Book of 99 with Revolut?

Yes, most top-tier Irish casinos like Paddy Power, Bet365, and BoyleSports fully support Revolut for both deposits and withdrawals in EUR. This allows for near-instant transactions, making it a very convenient choice for modern punters in the Republic. Using Revolut often means you can see your winnings in your account within minutes of requesting a withdrawal from the casino app.

What is the maximum win in EUR?

The maximum win is 12,075x your stake for the bonus feature, but a single spin can award up to 5,000x. If you are playing at the maximum bet of €100 per spin, the top single-spin payout is €500,000. For most casual players at a €1.00 stake, this means the top prize is a very impressive €5,000 hit, which is a significant result for any slot.

Is Book of 99 a high volatility slot?

Yes, the game is classified as having high volatility. This means that while it offers the potential for very large wins and has a high RTP, you can experience periods of dry spins. It is a game that rewards patience and careful bankroll management, as the payouts tend to be concentrated in the bonus round rather than the base game.

How do the expanding symbols work?

During the Free Spins round, one symbol is randomly chosen to be the special expanding symbol. If enough of these symbols land anywhere on the grid to form a win, they will expand vertically to cover all three positions on their respective reels, paying out across all 10 paylines. This can lead to the entire screen being filled with the same high-paying symbol for massive wins.

Does the collection meter reset if I change my bet?

The collection meter is tied to each specific bet level. If you change your stake, you will see a different meter reflecting your progress at that new level. However, your progress on the previous bet level is saved and will be waiting for you whenever you return to that specific EUR stake. This ensures that your progress is never lost even if you decide to change your strategy.

Is Book of 99 licensed in Ireland?

Yes, as long as you play at a casino licensed by the GRAI or the MGA. These regulatory bodies ensure that the game is fair, the 99% RTP is accurate, and that your funds and personal information are fully protected. It is always best to stick to these regulated sites to ensure you are playing in a safe environment.

Can I play Book of 99 for free?

Most Irish online casinos offer a "Demo" or "Play for Fun" mode for Book of 99. This allows you to experience the mechanics and see how the collection meter works without wagering any real EUR. It’s a great way to get a feel for the game's volatility and see how often the books land before you decide to play with real money.

Who developed Book of 99?

Book of 99 was developed by Relax Gaming, a well-known and highly respected provider in the iGaming industry. They are famous for their innovative mechanics and high-quality graphics, and Book of 99 is widely considered one of their most significant releases. They have a strong presence in the Irish market and are known for producing some of the most player-friendly titles in the industry.