rock oil vs petroleum

rock oil and petroleum both are nouns.

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

As nouns, rock oil and petroleum are synonyms defined as:

Other synonyms of rock oil include crude, crude oil, fossil oil, oil.

rock oil (noun)	petroleum (noun)
a dark oil consisting mainly of hydrocarbons	a dark oil consisting mainly of hydrocarbons