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 worldwide energy crisis which affected the
economies of consumer countries. One result of this
crisis has been that Britain has increased its North Sea oil
production and become the fifth largest oil producing
country in the world.