petroleum vs oil

petroleum and oil both are nouns.

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

As nouns, petroleum and oil are synonyms defined as:

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

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

petroleum: a dark oil consisting mainly of hydrocarbons
oil: a slippery or viscous liquid or liquefiable substance not miscible with water

Other hypernyms of petroleum include fossil fuel.

petroleum (noun)	oil (noun)
a dark oil consisting mainly of hydrocarbons	oil paint containing pigment that is used by an artist
	any of a group of liquid edible fats that are obtained from plants
	a slippery or viscous liquid or liquefiable substance not miscible with water
	a dark oil consisting mainly of hydrocarbons

petroleum (verb)	oil (verb)
	administer an oil or ointment to; often in a religious ceremony of blessing
	cover with oil, as if by rubbing