This is technique used by engineers to create a crack or fracture in the rock that contains oil or gas. This crack is then filled with sand or a artificial proppant (ceramic beads, sintered bauxite, or glass beads) to allow the freer flow of oil or gas from the rock to the wellbore. This processes is carried out using trucks equipped with high-pressure pumps and sand/proppant mixers (called “blenders”) mixing the proppant with an engineered “frac fluid” (usually a slimy looking watery substance) that is pumping down the well until the rock actually cracks or fractures. This fracture is extended a long distance from the well by pumping this proppant-loaded frac fluid at a high enough pressure to continue cracking the rock. When the process is complete, the well is closed and the fluid and proppant allowed to settle. The well is then reopened and the well is ready to test. There is a substantial amount of effort spent designing the correct type of frac job for a well. The cost to perform a frac job ranges from $50,000 to more than $1 million depending on the size and complexity of the job. Companies that perform this work are Schlumberger, Halliburton, BJ Services, Weatherford International, and others.