Crossword Genius

A worker in oils perhaps (7)

Ross

I believe the answer is:

refiner

I'm a little stuck... Click here to teach me more about this clue!

'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" .)

I've seen this clue in The Globe and Mail.
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