What Is Natural Gas?

Natural gas is the earth's cleanest fossil fuel and is colorless and odorless in its natural state. It is composed of four hydrocarbon atoms and one carbon atom (CH4 or methane).


Much of the natural gas we find and use today began as microscopic plants and animals living in shallow marine environments millions of years ago. As living organisms, they absorbed energy from the sun, which was stored as carbon molecules in their bodies. When they died, they sank to the bottom of the sea and were covered by layer after layer of sediment. As this organic feedstock became buried deeper in the earth, heat, combined with the pressure of compaction, converted some of the biomaterial into natural gas.


Once natural gas has been generated in nature, it tends to migrate within the sediments and rocks in which it was created, using the pore space, fractures and fissures that occur naturally in the subsurface. Some natural gas actually makes it to the surface and shows up in seeps, while other gas molecules travel until they are trapped or impeded by impermeable layers of rock, shale, salt or clay. These trapped deposits are the reservoirs where we find natural gas today.

The Earth's Cleanest Fossil Fuel

Natural gas is composed of four hydrogen atoms and one carbon atom (CH4 or methane). Colorless and odorless in its natural state, natural gas is the cleanest burning fossil fuel. When it burns, natural gas produces mostly carbon dioxide, water vapor and small amounts of nitrogen oxides.

Where Do We Find It?

Technological advances, an accessible and abundant domestic resource, and the world's most extensive and reliable delivery infrastructure have created a fundamental shift in the natural gas marketplace, providing an opportunity to satisfy significant new demand at affordable prices well into the future. In 2017, the Potential Gas Committee (Colorado School of Mines) in coordination with the American Gas Association (AGA), released a year-end 2016 biennial report: Potential Gas Supply of Natural Gas in the United States, which found thatthe United States possesses a technically recoverable natural gas resource base of 2,817 trillion cubic feet (Tcf) yet to be discovered. This is the highest resource evaluation in the Committee's 52-year history—a 12 percent increase from the previous high assessment from year-end 2014.

A Long History of Many Uses

The first use of gas energy in the United States occurred in 1816, when gaslights illuminated the streets of Baltimore, Md. By 1900, natural gas had been discovered in 17 states. During the years following World War II, expansion of the extensive interstate pipeline network occurred, bringing natural gas service to customers all over the country.

Today, natural gas is used extensively in residential, commercial and industrial applications. It is the main energy used for home heating: slightly more than half of American homes use gas. Increasingly, natural gas is being used for electric power generation as well.

A Little Goes a Long Way

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. A cubic foot of natural gas holds a lot of power, about 1,032 Btu. The unit you see on your heating bill holds even more power: most natural gas bills measure gas in therms, which is a unit of heating equal to 103,200 Btu. That's a lot of hot water! In fact, a therm is enough to provide almost 2.5 days of hot water for your household; and two therms can warm your home for a day.

Ten therms of natural gas is about enough to meet the natural gas needs of an average home — space heating, water heating, cooking, etc. — for five days.