Acutally, it's the other way around.<p><a href="http://en.wikipedia.org/wiki/Gasoline_gallon_equivalent#cite_note-0" rel="nofollow">http://en.wikipedia.org/wiki/Gasoline_gallon_equivalent#cite...</a><p>CNG is 5.660 pounds (2.567kg) per GGE.<p><a href="http://en.wikipedia.org/wiki/Gasoline#Density" rel="nofollow">http://en.wikipedia.org/wiki/Gasoline#Density</a><p>Gasoline is 6.073 pounds (2.755kg) per gallon.<p>I get the same economy (30-33 mpgge) in my Civic GX as in my gasoline Civic.<p>However, let's compare carbons based on molar mass (16.042 g/mol for methane and 100.21 g/mol for heptane and octane is 114.23g/mol). That's 160 moles of methane per GGE and 27.5 moles of heptane per gallon. That's a ratio of 160:192 of carbons. For octane, that's 24 moles per gallon, about the same ratio. It's not 1:4, granted, but these are just hand-wavey approximations for the gasoline, which has the added complication of ethanol. I'm also assuming <i>complete</i> burning, which is patently false, considering that, before modern emissions controls, it was possible to commit suicide by carbon monoxide poisoning from engine exhaust.<p>Edit: Molar mass