Ekofisk is an oil field in block 2/4 of the Norwegian sector of the North Sea about 320 km (200 mi) southwest of Stavanger.

The Ekofisk Center is a vast complex of platforms and structures creating a transportation hub also for surrounding fields such as Valhall, Hod, Gyda, Ula, Statfjord, Heimdal, Tommeliten and Gullfaks.

[9] "The reservoir rock...is a true chalk-a fine-grained limestone composed of the skeletal remains of pelagic unicellular golden-brown algae or coccolithophores".

[8] However, the high porosity of the reservoir rock does cause an increase in seismic amplitude which can be used with an isopach map to determine net pay.

Detailed geological investigation showed that it was the result of delayed compactional diagenesis of the Chalk Formation reservoir rocks.

The Norwegian government pressed Phillips to take action and the French company Technip was ordered to find a solution.

In April 1977, an oil well blowout occurred at the Ekofisk Bravo platform, due to an incorrectly installed downhole safety valve.