In fact, oil production is legendary (9)
I believe the answer is:
fictional
'legendary' is the definition.
(thesaurus)
'in fact oil production' is the wordplay.
'production' indicates anagramming the letters.
'in'+'fact'+'oil'='infactoil'
'infactoil' anagrammed gives 'FICTIONAL'.
'is' acts as a link.
(Other definitions for fictional that I've seen before include "Fabricated, imaginary" , "Made-up" , "Not true" , "Unreal" , "Invented; untrue" .)