residual oil vs rock oil

residual oil and rock oil both are nouns.

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

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

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

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