ONE of the biggest North Sea oil discoveries in recent years has been announced by US giant Chevron Texaco. It said it had made a 'significant oil and gas discovery' at the offshore Rosebank/Lochnagar well off the coast of Shetland. Alex Salmond, leader of the Scottish National Party and a former oil economist with Royal Bank of Scotland, claimed that the new field could hold the equivalent of 500m barrels of oil. He said: 'This is a significant new discovery and certainly a big find. It supports suggestions that there are still 50bn barrels there in the North Sea to be developed.'