The most common and most likely answer to this crossword clue is the 6 plus 3 letter word SULLOM VOE
S
U
L
L
O
M
V
O
E
Buddy explains!
The straight part
We know that "oil terminal" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case oil terminal = sullom voe.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.