Ship carrying petroleum (6)
I believe the answer is:
tanker
'ship carrying petroleum' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tanker that I've seen before include "Big ship for transporting oil" , "Ship or vehicle to carry crude oil" , "Vehicle or ship for carrying oil in bulk" , "Oil-carrier" , "Bulk liquid carrier" .)