It's a bit slow and inefficient, and also dangerous to do it at sea. So this is done only if space in the port is at premium. Which means only Hong Kong still

It's a bit slow and inefficient, and also dangerous to do it at sea. So this is done only if space in the port is at premium. Which means only Hong Kong still does this: http://en.wikipedia.org/wiki/Mid-stream_operation http://en.wikipedia.org/wiki/Mid-stream_operation