“Pirate oil tanker” is not a phrase that comes naturally to native English speakers, but we may want to practice saying it. A criminal enterprise with support from a rebel militia group in Libya managed to steal an oil tanker, load it with crude oil, and send it off to the open seas, although that is as far as they got. The BBC News story:
It used to be the assumption that anything as substantial a full-sized oil tanker would tend to be under civilized control, but not in this case. This was an unregistered ship with something close to a quarter billion dollars worth of oil. This might be the first story of its kind, but it is far from the first time pirates have taken control of an oil tanker. Over the last few centuries we have come to expect that large size is a sign of legitimacy, but that era may be ending.