Fluid Reservoirs are large deposits of fluid added by Immersive Petroleum that can be found under Bedrock. The only way to locate these reservoirs is by using a Core Sample Drill, and they can only be harvested using a Pumpjack. Each chunk has a chance to contain a Fluid Reservoir, including chunks in dimensions other than the Overworld. Each reservoir only takes up one chunk, and can range in size. Some types of fluid reservoirs may contain trace amounts of fluid even after being depleted, so a single Pumpjack may extract small amounts of fluid infinitely.
By default, there is a 50% chance for a chunk to contain a Fluid Reservoir.
Below is a table that shows each reservoir type included in the base mod, as well as its weight and contents (taken from the Engineer's Manual).
Crude Oil Bucket
|40||2,500,000 mB - 10,000,000 mB||6 mB / tick||Any dimension except the End|
|30||10,000,000 mB - 50,000,000 mB||6 mB / tick||Overworld|
|30||250,000 mB - 1,000,000 mB||None||Any dimension except the End|