The most common and most likely answer to this crossword clue is the 8 letter word RAPESEED
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More clues leading to the result RAPESEED
Buddy explains!

The straight part
We know that "potential source of oil" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case potential source of oil = rapeseed.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 RAPESEED mean?
RAPESEED noun- The seed of the rape plant, Brassica napus, used widely for animal feed and vegetable oil.
- The rape plant itself.