In Holland the discovery of an immense reservoir of natural gas has started what could be an economic and industrial revolution. Farther north, the Norwegians have found themselves being called 'The Libyans of Europe' because off-shore oil drilling seems certain to provide , them with four times their domestic needs. Tonight's film takes the viewer into a world where investment runs into thousands of millions of pounds and, at the same time, shows what it's like for the rough-necks and roustabouts, the divers and helicopter pilots who are taking part in one of the world's great treasure hunts. Reporter DONALD MACLEOD Producer JAMES WILSON (from Scotland)