Puzzle surrounding Mev's oil supplier (5)
I believe the answer is:
maize
'oil supplier' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'puzzle surrounding mev's' is the wordplay.
'puzzle' becomes 'maze' (I've seen this before).
'surrounding' is an insertion indicator.
'mev' becomes 'i' (I am not sure about this - if you are sure you should believe this answer much more).
'maze' going around 'i' is 'MAIZE'.
Can you help me to learn more?
(Other definitions for maize that I've seen before include "Indian corn" , "Type of corn" , "Plant producing sweetcorn" , "Something cultivated" , "Farm crop" .)