When they say "carbon" they really mean carbon dioxide, CO2.  Hence, the
weight of the "carbon" emissions exceeds the weight of the fuel, since the
fuel is a mixture of mostly carbon and hydrogen with a molecular weight of
12 for the carbon and 1 for the hydrogen atoms and oxygen has a molecular
weight of 16.  So, the short chain hydrocarbons in gas have a lower
molecular weight than CO2, which has a molecular weight of 44.  Obviously,
the weight of carbon emissions is calculated using molecular weight.

Stuart
BS Chemistry, UofW.  Gave it up 35 years ago.

Original message:

According to
http://www.environment.gov.au/settlements/transport/fuelguide/environment.ht
ml,
regular gas emits 2.3 kg of carbon per liter burned and diesel emits 2.7 kg
of carbon per liter.  (Don't ask me how the weight of the emissions can be
greater than the weight of the fuel burned, it doesn't make sense to me
either!)
Joy