According to the reports I read, this oil was a 'heavy crude'. Although not impossible, it would be difficult to get this stuff to start burning after it is in the water because the water begins to hydrate it and break it apart. Lighter crude is more volital and could catch on fire more easily but it too would be limited to a certain extent to the proximity of the tanker due to break up by the water and volitalzation of the oil.
Thanks Much and big SMILES