When testing and drilling demonstrate that a well is commercially viable, the completion process begins. A casing pipe is lowered into the well and cemented to the bottom and sides of the hole, temporarily sealing off production. A perforation jet gun is lowered into the hole. It perforates the casing and cement at intervals so oil and gas can enter the well bore.

Gas and oil are slow to emerge from most U.S. oil and gas wells; two methods of artificially stimulating the gas and oil from the rock formation are called fracturing and acidizing. During the process of fracturing, fluids are pushed under high pressure into the earth to crack open (fracture) a formation, providing a path for gas and oil to flow into the well.

During acidizing, acids are pushed into the earth, dissolving part of the rock and permitting oil and gas to flow into the well.