"pure gasoline is odourless. certain pungent additives are added to give gasoline that characterisitc smell, so that we can detect its presence with our nose easily."
I think that you're thinking of methane, a.k.a., natural gas. Gasoline (the stuff that goes in cars) has it's own odor--due to a lot of different chemicals going into it--like benzene, for instance. Gasoline is a pretty wide mix of chemicals, and even pure octane smells like something. However, natural gas does not. Methyl mercaptain is added to it (IIRC) to give it the characteristic odor.