Alexander L. Kielland was a Norwegian semi-submersible drilling rig that, on 27 March 1980, capsized in the Ekofisk oil field in the North Sea, killing 123 people.

Conditions were rainy with dense fog, with the wind gusting to 40 knots (74 km/h) and waves up to 12 metres (39 ft) high.

A fifth lifeboat came adrift and surfaced upside down; its occupants righted it and gathered nineteen men from the water.

Further, the investigation found considerable amounts of lamellar tearing in the flange plate and cold cracks in the underlying groove weld.

Judging by paint on part of the fractured surface, the crack was probably due to improper work during the rig's construction in 1976.

The rig was scuttled later that year in the Nedstrand Fjord after a search for missing bodies had been completed, as well as several tests to determine the cause of the disaster.

In response to the Kielland disaster, North Sea offshore installations tightened their command organization, identifying a clear authority who would order abandonment in case of emergency.

The fourteen minutes between initial failure of the leg and the rig's eventual capsize left a window in which most of the personnel on board could have escaped, had a more effective command structure been in place.

As a consequence, the International Maritime Organization issued a requirement for all lifeboats on merchant ships to be fitted with hooks that could be released even when they were under load.

[7] Not long after Kielland capsized, her sister rig, Henrik Ibsen, suffered a jammed ballast valve, causing her to list twenty degrees, but was later righted again.

[8] Approximately eighteen months later, Ocean Ranger capsized in similar weather conditions off the Newfoundland coast.

An investigation into the cause of the Ocean Ranger disaster by the United States Coast Guard established that structural failure was not a factor.