residual oil vs resid

residual oil and resid both are nouns.

Word	Noun	Adjective	Verb	Adverb
residual oil	Yes	No	No	No
resid	Yes	No	No	No

As nouns, residual oil and resid are synonyms defined as:

residual oil and resid: oil products that remain after petroleum has been distilled

residual oil (noun)	resid (noun)
oil products that remain after petroleum has been distilled	oil products that remain after petroleum has been distilled