The most common and most likely answer to this crossword clue is the 5 letter word MAIZE
I've seen this crossword clue in The Daily Telegraph
M
A
I
Z
E
More clues leading to the result MAIZE
- Crop of the month, do you say?
- Edible plant I found in labyrinth
- Crop one stored in old prison
- What's said to be West's staple food?
- Report month’s crop
- Grass one found in Hampton Court feature
- Grass puts Gaff in prison
- Grain, one in middle of confusing system
- Cereal heard with bewilderment
- Miss West’s heard about source of meal
Buddy explains!
The straight part
We know that "source of oil" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case source of oil = maize.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 MAIZE mean?
MAIZE noun- Corn; a type of grain of the species Zea mays.