unleaded gasoline vs petrol

unleaded gasoline and petrol both are nouns.

Word	Noun	Adjective	Verb	Adverb
unleaded gasoline	Yes	No	No	No
petrol	Yes	No	No	No

As nouns, petrol is a hypernym of unleaded gasoline; that is, petrol is a word with a broader meaning than unleaded gasoline:

unleaded gasoline: gasoline that has not been treated with a lead compound
petrol: a volatile flammable mixture of hydrocarbons (hexane and heptane and octane etc.) derived from petroleum; used mainly as a fuel in internal-combustion engines

Other hypernyms of unleaded gasoline include gas, gasolene, gasoline.

unleaded gasoline (noun)	petrol (noun)
gasoline that has not been treated with a lead compound	a volatile flammable mixture of hydrocarbons (hexane and heptane and octane etc.) derived from petroleum; used mainly as a fuel in internal-combustion engines