The most common and most likely answer to this crossword clue is the 8 letter word EUCALYPT
I've seen this crossword clue in The Times
E
U
C
A
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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 = eucalypt.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 EUCALYPT mean?
EUCALYPT noun- Any tree of the genus Eucalyptus.
- Any tree of the tribe Eucalypteae of genera related and similar to Eucalyptus, such as Corymbia and Angophora.