The term tight gas sands refers to low-permeability sandstone reservoirs that produce primarily dry natural gas. A tight gas reservoir is one that cannot be produced at economic flow rates or recover economic volumes of gas unless the well is stimulated by a large hydraulic fracture treatment and/or produced using horizontal wellbores. This definition also applies to coalbed methane, shale gas, and tight carbonate reservoirs. Tight sands produce about 6 tcf of gas per year in the United States, about 25% of the total gas produced. The Energy Information Administration estimates that 310 tcf of technically recoverable tight gas exists within the US, representing over 17% of the total recoverable gas. Worldwide, more than 7,400 tcf of natural gas is estimated to be contained within tight sands, with some estimates as large as 30,000 TCF.