Natural gas is a gaseous fossil fuel consisting primarily of methane but including significant quantities of ethane, propane, butane, and pentane—heavier hydrocarbons removed prior to use as a consumer fuel —as well as carbon dioxide, nitrogen, helium and hydrogen sulfide. Fossil natural gas is found in oil fields (associated) either dissolved or isolated in natural gas fields (non-associated), and in coal beds (as coalbed methane).
Natural gas is often informally referred to as simply gas, especially when compared to other energy sources such as electricity. Before natural gas can be used as a fuel, it must undergo extensive processing to remove almost all materials other than methane. The by-products of that processing include ethane, propane, butanes, pentanes and higher molecular weight hydrocarbons, elemental sulfur, and sometimes helium and nitrogen. – http://en.wikipedia.org/wiki/Natural_gas
Recently, individuals and companies with a financial stake in natural gas production have been engaged in an effort to re-brand natural gas as an ‘alternative’ fuel. Since in English the word ‘alternative’ describes any option that isn’t the standard or default, and natural gas is not the standard fuel for, say, cars and trucks, no one can write them a ticket for their highly elastic use of the word and concept. However, by the definition of the term as it has been used for decades, natural gas is not an alternative fuel. “Alternative fuels, also known as non-conventional fuels, are any materials or substances that can be used as a fuel, other than conventional fuels. Conventional fuels include: fossil fuels (petroleum (oil), coal, propane, and natural gas), and nuclear materials such as uranium. Some well known alternative fuels include biodiesel, bioalcohol (methanol, ethanol, butanol), chemically stored electricity (batteries and fuel cells), hydrogen, non-fossil methane, non-fossil natural gas, vegetable oil and other biomass sources.” – http://en.wikipedia.org/wiki/Alternative_fuel
In fact, natural gas is just another highly polluting hydrocarbon and conventional – that is, non-alternative – fuel like oil, to which it is closely related and with which it is frequently found. Further, extracting natural gas and transporting it to markets takes huge amounts of, you guessed it, (imported) oil.