Oil is definitely sold in the black markets. Anything that is in demand that has value is so why wouldn't oil be? One such black market is in Turkey which is strategically situated to be just perfect for the illegal trade. A loss of an estimated $5 billion inUS tax revenue last year resulted in the black market sales from Turkey alone and there are other countries that sell on the black market too.
Whenever there is a good thing, it seems there is a bad force too. Oil is a commodity that is good but there will always be those people who get their greedy hands on things and turn the good around. There is a black market on most anything that is of value an oil is for sure falls into that classification.