A worker in oils perhaps (7)
I believe the answer is:
refiner
'a worker' is the definition.
(refiner is a kind of worker)
'in oils perhaps' is the wordplay.
I cannot quite see how this works, but
'in' is present in the answer.
The remaining letters 'refer' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for refiner that I've seen before include "Oil processor" , "He clarifies" , "Oil worker" , "One who removes impurities (from metal)" , "Oilman" .)