residual oil vs petroleum

residual oil and petroleum both are nouns.

Word	Noun	Adjective	Verb	Adverb
residual oil	Yes	No	No	No
petroleum	Yes	No	No	No

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

Other hypernyms of residual oil include crude, crude oil, fossil oil, oil, rock oil.

residual oil (noun)	petroleum (noun)
oil products that remain after petroleum has been distilled	a dark oil consisting mainly of hydrocarbons