The most common and most likely answer to this crossword clue is the 9 letter word GROUNDNUT
I've seen this crossword clue in Independent
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Buddy explains!
The straight part
We know that "oil producer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case oil producer = groundnut.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does GROUNDNUT mean?
GROUNDNUT noun- A climbing vine, Apios americana, of eastern North America, having fragrant brownish flowers and small edible tubers.
- Any similar plant having underground tubers.
- The nutlike tuber of such a plant, especially peanuts.
- A plant which bears its nutlike seeds underground, such as a peanut or Bambara groundnut.