CN Rail (TSX:CNR) is considering shipping Alberta’s oil sands output to Prince Rupert, British Columbia, by train in quantities that match the proposed Northern Gateway pipeline.

Internal government documents obtained by Greenpeace (see images) under the access to information act, suggest Chinese-owned Nexen (TSX, NYSE:NXY) is already working with CN to ship oil by tanker to Asia.

But it looks like the train option is only a back-up plan, in case Enbridge’s $5.5 billion Northern Gateway project gets rejected.

The proposed ducts includes two pipelines running 1,177 kilometres to carry 525,000 barrels of oil per day from Alberta to BC's north coast.