gas oil vs heating oil

gas oil and heating oil both are nouns.

Word	Noun	Adjective	Verb	Adverb
gas oil	Yes	No	No	No
heating oil	Yes	No	No	No

As nouns, heating oil is a hypernym of gas oil; that is, heating oil is a word with a broader meaning than gas oil:

gas oil: an oil formed through distillation of petroleum of intermediate boiling range and viscosity
heating oil: a petroleum product used for fuel

Other hypernyms of gas oil include fuel oil, hydrocarbon.

gas oil (noun)	heating oil (noun)
an oil formed through distillation of petroleum of intermediate boiling range and viscosity	a petroleum product used for fuel