Petroleum reservoir

Petroleum reservoirs are large underground bodies of Crude Oil or Natural Gas, sealed with 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 reservoir edges are irregular. Reservoirs line up across chunk borders.

A reservoir only fills space that is already open (air, cave air and water), so it fills parts of caves and aquifers with oil or gas. It doesn't carve out stone. Every opening around the fluid except its open face is sealed with a bituminous block.

	Crude Oil reservoir	Natural Gas reservoir
Kind	Pool: fills open space up to a fluid level. The top surface is open.	Cap: fills open space down to a floor. 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 within 8 blocks of the surface.

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. If you find them while mining, oil or gas is usually next to 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.