Fossil Dig: how it plays, odds and payouts

Fossil Dig is a ladder game that goes down. You dig through five layers of rock, one cell per layer. Every find multiplies your take. A cave-in ends the dig and loses the bet. After any find you can crate it and keep your take, or dig on into the next layer.

Coins are virtual with no cash value.

How a round works

1. Pick a dig site: Shallow, Badlands or Deep Quarry. The sites differ in cave-in chance and in how big the finds are.
2. The site is a grid of 6 columns and 5 layers, and all 30 cells are drawn on our servers when the round starts. Tap a spot in the glowing layer, or tap Dig to go straight down.
3. A bone, amber, gem or the layer's rare fossil multiplies your take. A cave-in ends the dig with the bet lost.
4. Tap Crate it after any find to keep your take. Clearing the fifth layer, the Bone Bed, ends the round and pays the take in full.

At the end the whole site is shown, so you can see what the other columns held.

The five layers

The layers from top to bottom are Dune Crust, Red Sandstone, Ash Shale, Ironstone and the Bone Bed. Each has a different rare fossil: Trilobite, Ammonite, Raptor Claw, Horned Skull and the King Rex.

The chance of a cave-in rises with every layer you go down:

The rare fossil turns up in 1.2%, 1.0%, 1.0%, 0.8% and 0.6% of cells in the five layers, at every site. Gems range from 2.8% of cells in the top layer to as much as 10.3% lower down.

What it pays

Your take starts at your bet times 0.97, which is the 3% house edge, and each find multiplies it by its factor. Every layer is balanced so that the average factor of one dig is exactly 1, with a cave-in counted as zero. That is why no rule for when to crate returns more than 97% over time.

The chance of clearing all five layers without a cave-in is 30.1% at Shallow, 14.1% at Badlands and 3.7% at Deep Quarry.

Worked example

You bet 100 coins at Badlands. The first dig, in Dune Crust, finds amber (x1.6) and your take is about 155 coins. The second, in Red Sandstone, finds bone (x1.2) and the take is about 186. Crate it and you keep 186. Dig again and there is a 32% chance of a cave-in in Ash Shale that would lose all of it, against a chance of a bigger take if the dig goes well.

Max win and limits

The best result is the rare fossil in every layer, ending with the King Rex. That pays 4,190x at Shallow, 18,624x at Badlands and 40,740x at Deep Quarry. It is the same 1 in about 17 billion chance at every site, because the rare-fossil chances do not change between them. The game-wide limits (50,000x the bet, 250,000,000 coins per round) are not reached. Volatility is very high.

What matters and what does not

• Dig site: changes how swingy the game is, not the 97%.
• When you crate: changes the size of a win, not the long-run return.
• Which column: a choice of cell, not of odds. See Cash-Out Ladder Games: Road Hop, Tower and More for why ladder games price every step the same way.
• Pace: the cells were set at the start of the round, so tapping faster or slower changes nothing.

The published odds for every game are on the odds page.