Hydraulic fracturing carried out in the Barnett Shale is done by pumping a mixture of water, sand, and various chemical additives (to affect viscosity, flow rates, etc.) into the well bore at a sufficient pressure to create and propagate a fracture in the surrounding rock formation down hole. This is crucial in low permeability rock as it exposes more of the formation to the well bore and greater volumes of gas can be produced by the increased surface area. Without hydraulic fracturing, the wells would not produce at an economically feasible rate.