Considering the release during combustion alone greenhouse gas emissions from burning natural gas average 13.7 g C of CO2 per million joules of energy compared to 18.6 for gasoline 18.9 for diesel fuel and 24.0 for bituminous coal.
…but there’s more to it than that [url=http://www.sixdegrees.org.au/content/coal-seam-gas-no-solution-climate-change]here[/url]
and [url=http://www.eia.gov/oiaf/1605/coefficients.html]here[/url].