Acutally, it's the other way around. http://en.wikipedia.org/wiki/Gasoline_gallon_equivalent#cite_note-0 http://en.wikipedia.org/wiki/Gasoline_gallon_equivalen

Acutally, it's the other way around. http://en.wikipedia.org/wiki/Gasoline_gallon_equivalent#cite_note-0 http://en.wikipedia.org/wiki/Gasoline_gallon_equivalent#cite... CNG is 5.660 pounds (2.567kg) per GGE. http://en.wikipedia.org/wiki/Gasoline#Density http://en.wikipedia.org/wiki/Gasoline#Density Gasoline is 6.073 pounds (2.755kg) per gallon. I get the same economy (30-33 mpgge) in my Civic GX as in my gasoline Civic. 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 complete burning, which is patently false, considering that, before modern emissions controls, it was possible to commit suicide by carbon monoxide poisoning from engine exhaust. Edit: Molar mass