Programs of deep drilling in the North Sea since 1964, particularly within the sector under British jurisdiction, have established that the Southern, or English, basin is a major gas-bearing province and the Northern, or Norwegian, basin, showing every promise for additional significant discoveries, holds several commercial-size oil fields at close intervals through a wide range of latitude. The area held under license for the exploration and possible exploitation of these subsea petroliferous resources has been extended progressively to deeper and more remote waters. This has involved increased scales of investment and will continue to demand even greater advancements in recovery techniques to cope with a particularly hostile environment.

In the English basin, where exploration to date has proved the presence of some 35 Tcf of recoverable gas within British waters, the main reservoir rocks are within the sandy facies of the Lower Permian Rotliegendes Formation. The oil-bearing Norwegian basin has several productive zones, which include the Danian limestones of early Tertiary-Late Cretaceous ages in the southwestern corner of the sector held by Norway, the Paleocene sandstones at the base of the thick Tertiary sedimentary deposits east of the Aberdeenshire coast of Scotland, and sandstones of Jurassic age in the northerly extension into the East Shetland trough. Major discoveries in the latter area during 1973 and the first half of 1974 have helped notably to boost the estimates of proved recoverable reserves within the British sector of the North Sea to 10 to 13 billion bbl.

Geophysical and geologic data show that in addition to the North Sea, the central sectors of the English Channel forming the seaward extension of the Wessex basin, the Western Approaches to the English Channel, the Celtic Sea, the sea areas west of the Orkneys and Shetlands, and much of the outer Norwegian shelf are highly prospective. If continental drift occurred, the evolutionary history of the North Atlantic also points to the likely existence of sizable petroliferous accumulations beneath the contiguous continental slope.