Joined forces in petrol refining (8)
I believe the answer is:
interpol
'joined forces' is the definition.
(I've seen this before)
'petrol refining' is the wordplay.
I cannot quite see how this works, but
an anagram of 'petrol' is 'terpol' which is located in the answer.
The remaining letters 'in' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'in' is the link.
Can you help me to learn more?
(Other definitions for interpol that I've seen before include "detectives" , "International police force" , "Lyon-based Police Commission" , "Organisation for international police cooperation" , "Cross-border crimefighters" .)