crude oil vs petroleum

crude oil and petroleum both are nouns.

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

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

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

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