cartel vs oil cartel

cartel and oil cartel both are nouns.

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

As nouns, oil cartel is a hyponym of cartel; that is, oil cartel is a word with a more specific, narrower meaning than cartel:

cartel: a consortium of independent organizations formed to limit competition by controlling the production and distribution of a product or service
oil cartel: a cartel of companies or nations formed to control the production and distribution of oil

Other hyponyms of cartel include drug cartel.

cartel (noun)	oil cartel (noun)
a consortium of independent organizations formed to limit competition by controlling the production and distribution of a product or service	a cartel of companies or nations formed to control the production and distribution of oil