When reading 'gas', the client will have to figure out whether that is about a liquid, in which case it has to choose a colonial 'g' (when written with a British 'g' 'gas' always is a liquid). If the meaning is that of a gaseous substance, the client will have to do additional work to determine what kind of 'g' to write.

You seem to be misguided about British English, in which gas is actually gaseous and not in fact an abbreviation for petrol.