One can understand from the passage that further oil explorations ………

The great expansion in energy demand over recent years has been met to a large extent by petroleum oil. The total world reserves of petroleum oil are still uncertain since large parts of the world are still not fully prospected. The cutback in oil production and the rise in the price of Middle Eastern oil following the 1973 Arab-Israeli war unleashed a world-wide energy crisis has been that Britain has increased its North Sea oil production and become the fifth largest oil producing country in the world.