oil rig vs oilrig

oil rig and oilrig both are nouns.

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

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

Other synonyms of oil rig include drill rig, drilling rig.

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