Ann Pickard, the head of Royal Dutch Shell in Africa, pushes across her desk a map that appears to suggest Nigeria has broken out in an alarming rash.

Marking the location of oil and gas deposits, multi-coloured blobs pepper both land and sea, revealing the scale of untapped potential. "The future is huge," says Ms Pickard. "You can see a lot of gas, but surprisingly there's still a lot of oil left."