Significant hydrocarbon reserves approaching 16 billion bbl of oil and 145 Tcf of gas have been found in and adjacent to the North Sea since the discovery of Groningen field in 1959. Reserves are found in rocks ranging in age from Carboniferous to early Tertiary. This vast basinal area covers more than 280,000 sq mi and is bounded on the east by the Baltic shield, on the west by the Scottish Highlands, and on the south by the Hercynian metamorphic rocks of the Cornwall Peninsula and the Ardennes.

The basin, essentially floored by Caledonian metamorphic rocks, is highly structured, both by regional tectonic movements and by local salt mobility. Regional positive features, such as the Mid-North Sea high, the Ringkobing-Fyn-Falster high, and the Texel high divide the North Sea into several subbasins and have influenced regional sedimentation.

Three major regional unconformities provide a highly varied juxtaposition of rich source and excellent reservoir beds. Widely changing lithologies within the basinal area indicate the extremes of environmental conditions throughout its development.

The principal source of gas for the Permian and Triassic reservoirs is considered to be the underlying Carboniferous. The source for oil in the Mesozoic and Tertiary reservoirs is the associated organically rich shales of similar age.

Severe weather conditions and high operating costs have tended to retard exploration and development activities. Many potential structures remain to be drilled. There is reason to expect continued success in the discovery of additional hydrocarbon reserves.