Natural gas is a mixture of hydrocarbons- mainly methane (CH4) - and is produced either from gas wells or in conjunction with crude oil production. Natural gas is consumed in the residential, commercial, industrial, and utility markets.

Natural gas, like other forms of heat energy, is measured in British thermal units or Btu. One Btu is equivalent to the heat needed to raise the temperature of one pound of water by one degree Fahrenheit at atmosphere pressure.

A cubic foot of natural gas has about 1,027 Btu. Natural gas is normally sold from the wellhead in the production field to purchasers in standard volume measurements of thousands of cubic feet (Mcf). However, consumer bills are usually measured in heat content or therms. One therms is a unit of heating equal to 100,000 BTU.

Gas streams produced from reservoirs contain natural gas liquids and other materials. Processing is required to separate the gas from petroleum liquids and to remove contaminants. First, the gas is separated from free liquids such as crude oil, hydrocarbon condensate, water, and entrained solids. The separated gas is further processed to meet specified requirements. For example, natural gas for transmission companies must generally meet certain pipeline quality specifications with respect to water content, hydrocarbon dew point, heating value, and hydrogen-sulfide content. A dehydration plant controls water content; a gas processing plant removes certain hydrocarbon components to hydrocarbon dew point specifications; and a gas sweetening plant removes hydrogen sulfide and other sulfur compounds (when present).

Compressed natural gas (CNG) is the form in which natural gas is compressed into special high-pressure cylinders at a pressure of usually 3,000 - 3,600 pounds per square inch (psi). It's compressed to get more volume in a smaller amount of space in the cylinder, thereby allowing sufficient storage and eventually range for the vehicle. Compressed natural gas is often used in light-, medium-duty and some heavy-duty vehicle applications.

Cogeneration is the use of a primary energy - like natural gas - to sequentially produce heat and electricity. The concept is based on the recovery and use of waste heat produced during the generation of electricity. In most electric utility power plants, this waste heat is lost, resulting in substantially lower operating efficiencies than with cogeneration. Another contributing factor to the dominance of natural gas use in cogeneration systems is the clean-burning nature of gas. When compared with a similarly sized conventional coal or oil-based system with pollution control equipment, a gas-fueled turbine cogeneration system emits significantly less sulfur dioxide, particulates and nitrogen oxides. Many commercial and industrial facilities can take advantage of natural gas cogeneration because of their requirements for large quantities of heat and electricity. Natural gas-fueled cogeneration is being successfully applied in the pulp and paper, pharmaceutical, food processing, textile, oil refining, fertilizer and other petrochemical industries, as well as in hospitals, universities, hotels, computer centers and other commercial facilities.