oil rig vs drill rig

oil rig and drill rig both are nouns.

Word	Noun	Adjective	Verb	Adverb
oil rig	Yes	No	No	No
drill rig	Yes	No	No	No

As nouns, oil rig and drill rig are synonyms defined as:

Other synonyms of oil rig include drilling rig, oilrig.

oil rig (noun)	drill rig (noun)
rig used in drilling for oil or gas	rig used in drilling for oil or gas