* what do Americans call 'gas' not petrol but gas?
Americans call petrol "gas" or "gasoline". Currently averaging about $3.15/gallon. Price difference to Europe is mainly taxes.
Most gas in the US of A is 10% ethanol which is usually approx. 10 cents a gallon cheaper.
We also have E-85, which is 85% ethanol. This sells at quite a discount, $2.54/gallon.
The gas that you are referring to is Natural Gas or Nat Gas. Which is what we use to cook with and heat our homes. Not too many use Nat gas for transportation except maybe commercial fleet operators. LP gas is propane. This was more popular in the 1970's, last gas crisis.
When I was in England last (2006?) I rented a car and diesel was popular. Diesel in the states is mainly truck fuel, $3.75/gallon.