Cryptic crossword clue
Petroleum product derived from full isomer, oddly 4,3

The most common and most likely answer to this crossword clue is the 4 plus 3 letter word FUEL OIL

I've seen this crossword clue in Financial Times
F
U
E
L
O
I
L

Buddy explains!

The straight part
We know that "Petroleum product" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case petroleum product = fuel oil.
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.

Crossword Answer definitions

Latest crossword clues with full explanations