Before production starts a site must be surveyed, environmental impact studies may be done, lease agreements, titles, and right-of way accesses for the land must be obtained, and, for off-shore sites, legal jurisdiction must be determined. The drilling process then begins. Only about 30 percent of the contents of a typical oilfield are ever brought to the surface.

For on-shore sites, water is crucial, so if no natural source exists, a well is dug. A reserve pit is also dug to dispose of rock cuttings and drilling mud. A rectangular pit —- a cellar -— is dug around the actual drilling hole to accommodate the workers and drilling accessories. The rig is set up and drilling begins. On-shore wells can be quite shallow, only hundreds of feet deep, to very deep, in excess of 20,000 feet. Typically, drilling is vertical although over the past several decades directional drilling has become more common. Drilling is done in stages: as the hole deepens, it is flushed with mud and its sides are filled with a metal casing and cement to keep the walls from collapsing. Once the depth is reached where oil is expected, explosives are used to perforate the well casing. A multi-valve device-— a Christmas tree -—is attached to the wellhead to control flow. Either acid is pumped into the well bottom to dissolve the rock containing the oil or a pressurized slurry is pumped in to further perforate the casing. The drilling rig is then removed and replaced with a pump and production begins. Drilling produces more than just oil; it has three very unwelcome and unmarketable by-products: brine, drilling muds and cuttings, and atmospheric pollution.