SEED Science

The Making of Oil:
Birth of a Reservoir

Rise and Fall of the North Sea


300 Million years ago

200 Million years ago

100 Million years ago


Today, North Sea oil lies under 300 feet of water, and a mile or more below the sea floor. But the oil was formed over millions of years in a dramatically different place....

Three hundred million years ago, the present-day North Sea was unrecognizable. What is now deep water was a shallow sea, shown in light blue. Wherever you see light blue, oil was forming under organic-rich waters. Where you see dark blue -- deep water -- shales were laid down, which helped trap oil.

The coastlines shifted dramatically as sea level rose and fell. What is now under water might have been dry land, and vice versa.

Volcanoes ejected blankets of ash and lava that trapped oil. Great sand dunes swept northward, and formed sandstone that would hold oil.

Today, more than 150 oil fields dot the North Sea, from The Netherlands to the Shetland Islands. No two fields are exactly the same, but all owe their birth to the rise and fall of sea level over millions of years.

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