Last updated: May 2026. Specs cross-verified against the Relax Gaming official product page, in-game info panels at the four featured AU casinos, and independent slot-database listings.
Book of 99 is the kind of pokie where the specs matter more than the screenshots. The visual is a competent but ordinary Greek-mythology book slot — marble columns, Orpheus, his lyre, scrolling parchment. What sets it apart is one number: 99% RTP. This article lays out every spec a serious player wants to see — provider, release, math, variance, paytable, hit frequency, bonus math, and the practical implications of each.
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Headline specs
| Spec | Value |
|---|---|
| Game name | Book of 99 |
| Provider | Relax Gaming |
| Release date | 4 May 2021 |
| Game type | Video slot, book/expanding-symbol genre |
| Grid | 5 reels × 3 rows |
| Paylines | 10 fixed, left-to-right |
| RTP | 99% (market-leading) |
| Volatility | High |
| Hit frequency | ~23% (base game) |
| Free-spin trigger frequency | ~1 in 220 spins |
| Max win | 12,075× stake |
| Bet range (AUD) | A$0.10 – A$100 |
| Min coin value | 0.01 |
| Bonus Buy | Yes (~100× stake, where supported) |
| Free spins | 10, with one expanding symbol |
| Wild symbol | Golden book |
| Scatter symbol | Golden book (same symbol acts as both) |
| Demo mode | Yes |
| Mobile | iOS, Android, browser (HTML5) |
| Languages | 20+ |
| Currency support | AUD, EUR, GBP, USD, CAD + 20 more |
| RNG certification | iTech Labs / GLI |
| MGA licence | Relax Gaming, Malta |
RTP — the headline number
99% RTP is the number that separates Book of 99 from every other mainstream pokie. The house edge is just 1%. For comparison:
| Slot | RTP | House edge |
|---|---|---|
| Book of 99 (Relax) | 99% | 1% |
| Book of Dead (Play'n GO) | 96.21% | 3.79% |
| Book of Ra Deluxe (Novomatic) | 95.1% | 4.9% |
| Sweet Bonanza (Pragmatic) | 96.51% | 3.49% |
| Starburst (NetEnt) | 96.09% | 3.91% |
| Gates of Olympus (Pragmatic) | 96.5% | 3.5% |
The gap matters. On a A$100 spin budget, Book of 99 expects to return A$99 over the long run. Book of Ra Deluxe expects to return A$95.10. That's a difference of roughly A$3.90 per A$100 spun in your favour — and it compounds across a long session.
RTP variant caveat: Relax Gaming publishes the game with multiple RTP builds. The 99% flagship is the default. Lower variants (96%, 94%, 92%) exist for casinos in less-regulated jurisdictions. Always verify in the game's info panel before depositing. See our 99% RTP math breakdown for what the headline number actually buys you.
Volatility — what high variance actually feels like
Relax Gaming officially rates Book of 99 as high volatility. In practical terms:
- Base-game hit frequency is ~23% — roughly one in four spins lands at least a small win.
- Most of those small wins are below your stake. Truly profitable base-game spins are rare.
- The free-spin trigger hits roughly once every 220 spins on average.
- Free-spin outcomes are heavily skewed: most rounds land below 50× stake, a small fraction land above 500×, an even smaller fraction reach the multi-thousand-× range.
What this means for you: expect dry stretches of 50-100 spins between meaningful wins, even with 99% RTP. The high RTP is real, but it's delivered through the bigger bonus payouts, not through more frequent small wins. If you want consistent small wins, this isn't the game — try a low-variance slot like Starburst.
Paytable — high-pays and low-pays
Per single payline, with all symbols at maximum (5-of-a-kind), based on bet of 10 coins:
| Symbol | 3-of-a-kind | 4-of-a-kind | 5-of-a-kind |
|---|---|---|---|
| Orpheus (top high-pay) | 1× | 4× | 10× |
| Lyre | 0.5× | 2× | 5× |
| Winged helm | 0.5× | 2× | 5× |
| Snake | 0.4× | 1.5× | 4× |
| Ace | 0.2× | 1× | 2.5× |
| King | 0.2× | 0.8× | 2× |
| Queen | 0.2× | 0.8× | 2× |
| Jack | 0.1× | 0.5× | 1.5× |
| 10 | 0.1× | 0.5× | 1.5× |
| Golden book (wild/scatter) | 2× | 20× | 200× |
The paytable looks modest in the base game because most of the RTP is delivered through the free-spins round. A 5-of-a-kind Orpheus on the base game is 10× stake. The same Orpheus expanding to fill all five reels during free spins is 1,000×+ stake when it pays on every line. That's the math design.
Bonus round math
Trigger: 3+ golden books anywhere on the reels.
Award: 10 free spins + one randomly selected expanding symbol.
Expanding-symbol distribution (approximate):
| Selected symbol | Probability | Typical round value |
|---|---|---|
| 10, J, Q, K, A (card ranks) | ~70% | 5×–50× stake |
| Snake / Helm / Lyre (mid-pays) | ~25% | 50×–500× stake |
| Orpheus (top high-pay) | ~5% | 100×–12,075× stake |
The Orpheus expanding symbol is the path to the max win. It's also rare — roughly 1 in 20 bonus rounds. Combined with a 1-in-220 trigger frequency, that's ~1 in 4,400 spins for an Orpheus bonus round. Reaching the 12,075× ceiling requires both Orpheus selected AND it landing on multiple reels in a single round, which is rarer still.
Retrigger: 3+ books during free spins = +10 spins. Same expanding symbol carries through retriggers. The full free-spins payout distribution maps what each round shape typically returns.
Max win — 12,075× stake
The max-win ceiling is 12,075× stake. The route is the free-spins round with Orpheus selected as the expanding symbol, landing on all five reels in a single spin. From a A$10 bet, that's A$120,750 in one spin.
This is the documented theoretical ceiling. In practice, most max-win clips on YouTube come from sessions where Orpheus expanded on 4 or 5 reels across multiple free spins, accumulating to near-ceiling totals. A single-spin 12,075× hit is the rarest version of an already-rare event — our max-win odds and stake-sizing analysis covers the realistic path.
Bonus Buy
Where supported (most AU-facing casinos enable it), Bonus Buy lets you pay roughly 100× your current stake to trigger the free-spins round directly.
| Stake | Bonus Buy cost |
|---|---|
| A$0.20 | A$20 |
| A$1.00 | A$100 |
| A$5.00 | A$500 |
| A$10.00 | A$1,000 |
RTP of the Bonus Buy: typically same 99%, though some studios reduce it slightly on Bonus Buy paths. Verify in the casino's specific build before using.
Bet range and coin denominations
| Setting | AUD value |
|---|---|
| Min coin value | A$0.01 |
| Max coin value | A$10 |
| Min bet per spin | A$0.10 |
| Max bet per spin | A$100 |
| Auto-spin range | 10 – 1,000 spins |
10 fixed paylines means your bet is always divided across 10 lines. A A$1 bet = A$0.10 per line.
Mobile and platform specs
- HTML5 — runs in any modern browser.
- iOS: Safari, Chrome (iOS). Tested iPhone 12 and newer.
- Android: Chrome, Samsung Internet. Tested Pixel 6+, Galaxy S22+.
- Tablet: iPad, Android tablets — landscape mode unlocks larger animations.
- Frame rate: 60fps on flagship devices, 30fps fallback on older.
- Data usage: ~150-200 MB per hour of play.
RNG and licensing
- RNG certification: iTech Labs and GLI (Gaming Laboratories International).
- Studio licence: Malta Gaming Authority (MGA), held by Relax Gaming Limited.
- Game integrity: Independent third-party audited every 12 months per MGA requirements.
How Book of 99's specs compare to other Relax titles
Relax Gaming's catalogue is broad. Book of 99 sits at the high-RTP, high-volatility end:
| Game | RTP | Volatility | Max win |
|---|---|---|---|
| Book of 99 | 99% | High | 12,075× |
| Money Train 4 | 96.1% | Extreme | 150,000× |
| Money Cart 4 | 95% | Extreme | 50,000× |
| Hellcatraz 2 | 96.4% | High | 51,840× |
| Beast Mode | 95% | High | 12,500× |
Most Relax titles sit in the 95-96% range. Book of 99 is the outlier — built deliberately as a high-RTP showcase title.
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Quick FAQ
Is the 99% RTP guaranteed at every casino? No. Casinos can deploy lower RTP variants. Always verify in-game.
Why is hit frequency only 23% with 99% RTP? Because the RTP is delivered through bigger but rarer wins. Hit frequency and RTP are independent metrics.
Does Bonus Buy have the same RTP as natural play? Usually 99% on the buy path too, though some builds vary slightly. Check the in-game info panel.
Is Book of 99 actually the highest RTP slot? It's the highest-RTP mainstream video slot in regulated markets. A handful of niche games claim higher, but among modern slots from Tier-1 studios, Book of 99 leads.
Where do I verify the specs? In-game info panel (i icon, bottom-left), plus the Relax Gaming official product page.
About these specs
All values verified against the Relax Gaming official product page, in-game info panels at our four featured AU casinos during April-May 2026, plus cross-checks at SlotCatalog and AskGamblers databases.
Gambling responsibly. Specs are specs — they're not promises. 99% RTP is a long-term mathematical expectation, not a guarantee for your session. AU support: gamblinghelponline.org.au · BetStop · 18+ only.
Further Reading
Related reading in this guide: