natural gas

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A mixture of hydrocarbon gases that occurs with petroleum deposits, principally methane together with varying quantities of ethane, propane, butane, and other gases, and is used as a fuel and in the manufacture of organic compounds.

from the GNU version of the Collaborative International Dictionary of English.

• noun The combustible gas found associated with petroleum deposits, and also in other geological formations, comprised predominantly of methane plus variable other constitutents. It is an important source of energy, and is transported long distances by pipelines, or in a liquefied state in tankers, for commercial distribution. Some natural gas deposits contain helium, and comprise the primary source of that rare element.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun a mixture of gaseous hydrocarbons associated with petroleum deposits; mostly methane with smaller amounts of ethane, propane and butane; principally used as a fuel

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a fossil fuel in the gaseous state; used for cooking and heating homes