Gas????

We use "gas" as short for gasoline because that's usually the most common contexual usage such as "gas is expensive these days", or "I filled it up with 3 gallons of gas".

We call natural gas "natural gas" in labels and text, but just gas in normal uage, but usage is again highly contextual such as "I turned the gas on, but the flames didn't start", or standing in the kitchen and say "I smell gas. Is the stove turned off?".

American English is confusingly contextual sometimes, but a lot less than Japanese. According to Brin's Uplift novels, this chaoticness is a "good" thing for creativity.

 

And then there's the leguminous gas...

 

Guess we call gasoline gas for the same reason that you folks down under call a barbeque a barbie!

 

Gas is short for Gasoline, which is what cars generally combust for propulsion.

Petrol is short for Petroleum, which is a thick, flammable, yellow-to-black mixture of gaseous, liquid, and solid hydrocarbons that occurs naturally beneath the earth's surface, can be separated into fractions including natural gas, gasoline, naphtha, kerosene, fuel and lubricating oils, paraffin wax, and asphalt and is used as raw material for a wide variety of derivative products.

I don't put that in my car.

Unless I'm wrong and Petrol is short for Petrolatum, but then I don't put that in my car either.

Well, if it comes out of the ground we call it Natural Gas. If it is liquified we call it Liquified natural Gas. If it's a distilled product from petroleum we call it Propane, or Butane, depending on it's composition. If you Liquify Propane you get LPG.