Petroleum reservoir
Petroleum reservoirs are large underground bodies of Crude Oil or Natural Gas, sealed in the rock by bituminous blocks. Smaller petroleum caves are cave systems completely filled with one of the two fluids. Both were added in 0.5 Alpha 2 (1.21.1, 26.1.2 and 26.2) and generate in every Overworld biome.
For the exact numbers, see Feature generation/1.21.1-0.5 Alpha 2.
Reservoirs
Reservoirs work like vanilla's aquifers. The underground is divided into an invisible grid of cells, each 32 blocks wide and 16 blocks tall. Every cell has a fixed chance of being a reservoir, decided by the world seed, and each block belongs to the cell whose (randomly offset) centre is nearest. The borders between cells are bent by noise, so reservoirs have irregular, natural-looking edges instead of straight walls. Because every chunk works the answer out the same way, a reservoir lines up cleanly across chunk borders.
A reservoir only fills space that is already open: air, cave air and water inside its cells. In practice, it turns parts of caves and aquifers into oil or gas. Solid stone is never carved away. Every opening around the fluid, apart from its open face, is sealed with a bituminous block so that the fluid stays in place.
| Crude Oil reservoir | Natural Gas reservoir | |
|---|---|---|
| Kind | Pool: fills open space up to a fluid level, like a buried lake. The top surface is open. | Cap: fills open space down to a floor, like gas trapped under a ceiling. The bottom surface is open. |
| Height band | Y -48 to 32 | Y -56 to 16 |
| Chance per cell | 8% | 6% |
| Fluid level / floor | A random level from a quarter of the way up the cell to its top | A random floor in the lower three quarters of the cell |
Neither kind comes closer than 8 blocks to the surface, so reservoirs never break out into the open.
Petroleum caves
Each chunk has a small chance to start a short cave system using vanilla's cave shape. The whole cave is filled with source blocks, and every opening is sealed with bituminous blocks.
| Cave | Chance per chunk | Height range |
|---|---|---|
| Crude Oil cave | 2% | Y -40 to 30 |
| Natural Gas cave | 1.5% | Y -48 to 16 |
Bituminous blocks
Reservoirs, petroleum caves and (since Alpha 2) Crude Oil lakes are sealed with bituminous blocks. The block placed depends on what is underneath each position:
- Bituminous Sand where the ground below is sand
- Bituminous Red Sand where the ground below is red sand
- Bituminous Gravel everywhere else
Bituminous blocks are mined with a shovel. Seeing them while mining is a good sign that oil or gas is right behind them. All three can be processed in a Crusher (200 ticks):
| Input | Output |
|---|---|
| Bituminous Sand | 5 Bitumen + 3 Sand Dust |
| Bituminous Red Sand | 5 Bitumen + 3 Sand Dust |
| Bituminous Gravel | 5 Bitumen + 25% chance of 1 Gravel |
Extracting the fluid
Source blocks can be picked up with a bucket. For a whole reservoir, place a Pump directly above the fluid. The Pump takes whichever fluid is directly below it, then works through a 45 × 45 block area (22 blocks in every direction) one layer at a time, down to the bottom of the world, collecting 1,000 mB for each source block of that fluid and removing it.