Natural gas is composed of a combustible mixture of hydrocarbon gasses, primarily methane, and in its purest form, is colorless, odorless, and shapeless.  When burned, natural gas gives off a great deal of energy.  Ethane, butane, and propane are hydrocarbon gasses that can be found in coal in varying amounts, in addition to the large quantity of methane found in coal-beds.  These hydrocarbons can be extracted from the coal-bed, leaving predominantly methane gas.  In comparison to other fossil fuels, natural gas is clean burning, emitting lower levels of potentially harmful byproducts, particularly carbon dioxide and nitrogen oxides, in the air.

Historically, the vast majority of the nation's natural gas production has been derived from conventional reservoirs.  Conventional reservoirs form when porous and permeable strata are situated such that they trap the natural gas as it migrates toward the surface from deeper source rocks.  Conventional gas reservoirs often occur as rich pools of gas capping structurally high positions in otherwise water-saturated reservoirs.  Once a gas pool has been delineated, the relatively high porosity and permeability of the reservoir allows a large percentage of the gas to be extracted.   

Unconventional reservoirs are typically less financially sound and not as easily accessible as conventional reservoirs. The three predominant forms of unconventional natural gas that contribute significantly to the supply of natural gas are, tight gas sands, gas shales, and coal-bed methane.  Unconventional natural gas accounts for roughly 25% of total U.S. gas production.  More about coal-bed methane

Technological advances within the past 15 years have precipitated an increase in exploration activity for, and the development of, natural gas resources.  

According to the Annual Energy Outlook 2005 Overview, "U.S. natural gas consumption is projected to grow from 22 trillion cubic feet in 2003, to almost 31 trillion cubic feet in 2025."  " Total demand for natural gas is projected to increase at an average annual rate of 1.5 percent from 2003 to 2025, primarily as a result of increasing use for electricity generation and industrial applications, which together account for about 75 percent of the projected growth in natural gas demand from 2003 to 2025." 

Sources: naturalgas.org & AEO 2005 Overview